fix(client/netproto): align monster movement speed with 1.13c MonStats velocity and D2GS 0x67/0x68 nVelocity

src/client/session/online-session.ts

@@ -71,6 +71,7 @@ import { getViewportProfile } from '../view/viewport-profile.ts'
 import { ClientWorld, type ChatLogEntry } from '../world/client-world.ts'
 import { getCanonicalItemDataTables } from '../world/item-tables-provider.ts'
 import { OutboundRateLimiter } from './rate-limiter.ts'
+import { computeMonsterMoveSpeedSubTilesPerSec } from '../../common/units/monsters-data.ts'
 import { isTownLevel } from '../../common/world/scene-population.ts'
 
 export type OnlineSessionPhase =
@@ -1205,6 +1206,17 @@ export class OnlineSession {
             : { x: 0, y: 0 }),
       } as ServerEvent
     }
+    const preMoveUnit =
+      ev.type === 'UnitMove'
+        ? this.world.getUnit(
+            (evAny.unitType ?? ev.unitType) as UnitType,
+            Number(evAny.id ?? evAny.unitId ?? 1),
+          )
+        : undefined
+    const preMoveUnitPos =
+      preMoveUnit !== undefined && (preMoveUnit.x !== 0 || preMoveUnit.y !== 0)
+        ? { x: preMoveUnit.x, y: preMoveUnit.y }
+        : undefined
     this.world.apply(ev)
 
     if (
@@ -1371,10 +1383,49 @@ export class OnlineSession {
         const unit = this.world.getUnit(evTypeId as UnitType, evUnitId)
         const rawToX = Number(evAny.to?.x ?? evAny.targetX ?? evAny.x ?? 0)
         const rawToY = Number(evAny.to?.y ?? evAny.targetY ?? evAny.y ?? 0)
-        const toX = unit?.targetX !== undefined && (rawToX === 0 || evAny.target !== undefined) ? unit.targetX : rawToX
+        let toX = unit?.targetX !== undefined && (rawToX === 0 || evAny.target !== undefined) ? unit.targetX : rawToX
-        const toY = unit?.targetY !== undefined && (rawToY === 0 || evAny.target !== undefined) ? unit.targetY : rawToY
+        let toY = unit?.targetY !== undefined && (rawToY === 0 || evAny.target !== undefined) ? unit.targetY : rawToY
-        const fromX = evAny.from?.x ?? evAny.currentX ?? evAny.x
+        if (
-        const fromY = evAny.from?.y ?? evAny.currentY ?? evAny.y
+          ev.target &&
+          ((rawToX === 0 && rawToY === 0) ||
+            (ev.from !== undefined && rawToX === ev.from.x && rawToY === ev.from.y))
+        ) {
+          const targetTypeId = unitTypeToId(ev.target.unitType)
+          const isTargetLocalPlayer =
+            targetTypeId === 0 && (ev.target.id === this.world.selfId || this.world.selfId === 0)
+          if (isTargetLocalPlayer) {
+            const predSnap = this.predictor.getSnapshot()
+            if (predSnap.x !== 0 || predSnap.y !== 0) {
+              toX = predSnap.x
+              toY = predSnap.y
+            }
+          } else {
+            const targetInterp = this.interpolator.getEntityState(targetTypeId, ev.target.id)
+            if (targetInterp && (targetInterp.x !== 0 || targetInterp.y !== 0)) {
+              toX = targetInterp.x
+              toY = targetInterp.y
+            }
+          }
+          if (unit && (toX !== 0 || toY !== 0)) {
+            unit.targetX = toX
+            unit.targetY = toY
+          }
+        }
+        const explicitFromX = evAny.from?.x ?? evAny.currentX ?? evAny.x
+        const explicitFromY = evAny.from?.y ?? evAny.currentY ?? evAny.y
+        const existingInterp = this.interpolator.getEntityState(evTypeId, evUnitId)
+        const fromX =
+          explicitFromX !== undefined
+            ? Number(explicitFromX)
+            : !existingInterp && preMoveUnitPos !== undefined
+              ? preMoveUnitPos.x
+              : undefined
+        const fromY =
+          explicitFromY !== undefined
+            ? Number(explicitFromY)
+            : !existingInterp && preMoveUnitPos !== undefined
+              ? preMoveUnitPos.y
+              : undefined
         const isLocalPlayer =
           evTypeId === 0 && evUnitId === this.world.selfId && this.world.selfId !== 0
         if (unit && unit.unitType === 'player') {
@@ -1396,22 +1447,41 @@ export class OnlineSession {
             this.verifyLocalPlayerPosition(toX, toY, { kind: 'player-stop' })
           }
         } else if (ev.mode === 'stop') {
-          this.interpolator.stopEntity({
+          const motionState = this.interpolator.stopEntity({
             unitType: evTypeId,
             unitId: evUnitId,
             x: toX,
             y: toY,
           })
+          if (unit) {
+            unit.x = motionState.x
+            unit.y = motionState.y
+            unit.direction = motionState.dir64
+          }
         } else {
-          this.interpolator.startMove({
+          const speedSubTilesPerSec =
+            evTypeId === 1
+              ? computeMonsterMoveSpeedSubTilesPerSec(
+                  unit?.classId ?? 0,
+                  ev.mode === 'run',
+                  ev.velocityPercent,
+                )
+              : undefined
+          const motionState = this.interpolator.startMove({
             unitType: evTypeId,
             unitId: evUnitId,
-            ...(fromX !== undefined ? { currentX: Number(fromX) } : {}),
+            ...(fromX !== undefined ? { currentX: fromX } : {}),
-            ...(fromY !== undefined ? { currentY: Number(fromY) } : {}),
+            ...(fromY !== undefined ? { currentY: fromY } : {}),
             targetX: toX,
             targetY: toY,
             running: ev.mode === 'run',
+            ...(speedSubTilesPerSec !== undefined ? { speedSubTilesPerSec } : {}),
           })
+          if (unit) {
+            unit.x = motionState.x
+            unit.y = motionState.y
+            unit.direction = motionState.dir64
+          }
         }
         break
       }
@@ -1516,6 +1586,8 @@ export class OnlineSession {
       this.predictor.setDirection(selfUnit.direction)
     }
 
+    this.world.tick(dtMs, nowMs)
+
     this.interpolator.update(safeDt)
     for (const state of this.interpolator.getAllStates()) {
       const unit = this.world.getUnit(state.unitType as UnitType, state.unitId)
@@ -1544,19 +1616,19 @@ export class OnlineSession {
             unit.mode = unitInTown ? 5 : 1
             unit.moveMode = 'stop'
           }
-        } else if (
+        } else if (unit.unitType === 'monster' && unit.lifePct > 0) {
-          unit.unitType === 'monster' &&
+          if (state.moving && !unit.castState && unit.moveMode !== 'stop') {
-          !state.moving &&
+            unit.mode = state.running ? 15 : unit.moveMode === 'knockback' ? 9 : 2
-          unit.lifePct > 0 &&
+          } else if (
-          (unit.mode === 2 || unit.mode === 9 || unit.mode === 15)
+            !state.moving &&
-        ) {
+            (unit.mode === 2 || unit.mode === 9 || unit.mode === 15)
-          unit.mode = 1
+          ) {
-          unit.moveMode = 'stop'
+            unit.mode = 1
+            unit.moveMode = 'stop'
+          }
         }
       }
     }
-
-    this.world.tick(dtMs, nowMs)
     this.syncActiveAreaFromPlayerPosition({ emitHudSync: true })
   }
 

src/client/world/client-unit.ts

@@ -70,6 +70,8 @@ export class ClientUnit {
   targetY?: number | undefined
   targetUnit?: UnitRef | undefined
   moveMode?: 'walk' | 'run' | 'knockback' | 'stop' | undefined
+  velocityPercent?: number | undefined
+  pathType?: number | undefined
   mode: number
   direction: number
   lifePct: number

src/client/world/client-world.ts

@@ -49,6 +49,7 @@ import {
   type CharacterAnimSpeedParams,
 } from '../../common/units/char-anim-speed.ts'
 import { dir64FromPoints } from '../../common/units/direction.ts'
+import { computeMonsterMoveSpeedSubTilesPerSec } from '../../common/units/monsters-data.ts'
 import { isTownLevel } from '../../common/world/scene-population.ts'
 import {
   ClientUnit,
@@ -1535,8 +1536,7 @@ export class ClientWorld {
     }
 
     // Continuous unit movement interpolation across display frames
-    const step = (safeDt / 1000) * 10
+    if (safeDt > 0) {
-    if (step > 0) {
       const inTown = isTownLevel(this.areaId)
       for (const unit of this._units.values()) {
         if (unit.dead || unit.castState || unit.unitType === 'missile') continue
@@ -1545,6 +1545,16 @@ export class ClientWorld {
         const dy = unit.targetY - unit.y
         const dist = Math.hypot(dx, dy)
         if (dist === 0) continue
+        const speedSubTilesPerSec =
+          unit.unitType === 'monster'
+            ? computeMonsterMoveSpeedSubTilesPerSec(
+                unit.classId,
+                unit.moveMode === 'run',
+                unit.velocityPercent,
+              )
+            : 10
+        const step = (safeDt / 1000) * speedSubTilesPerSec
+        if (step <= 0) continue
         if (dist <= step) {
           unit.x = unit.targetX
           unit.y = unit.targetY
@@ -1701,6 +1711,8 @@ export class ClientWorld {
           x: Number(ev.targetX ?? ev.x ?? 0),
           y: Number(ev.targetY ?? ev.y ?? 0),
         },
+        ...(ev.velocityPercent !== undefined ? { velocityPercent: Number(ev.velocityPercent) } : {}),
+        ...(ev.pathType !== undefined ? { pathType: Number(ev.pathType) } : {}),
       }
     } else if (ev.type === 'ChatMessage') {
       ev = {
@@ -1903,6 +1915,12 @@ export class ClientWorld {
         unit.targetUnit = ev.target
         const moveMode = ev.mode ?? 'walk'
         unit.moveMode = moveMode
+        if (ev.velocityPercent !== undefined) {
+          unit.velocityPercent = ev.velocityPercent
+        }
+        if (ev.pathType !== undefined) {
+          unit.pathType = ev.pathType
+        }
         if (prevX !== targetX || prevY !== targetY) {
           unit.direction = dir64FromPoints(prevX, prevY, targetX, targetY, unit.direction)
         }

src/common/units/monster-mapping.ts

@@ -1515,6 +1515,75 @@ export const MONSTER_HCIDX_TO_ID: Readonly<Record<number, string>> = {
   733: "willowisp8",
 }
 
+/**
+ * Canonical 1.13c `MonStats.txt` `[Velocity, Run]` pairs indexed by `hcIdx` (0..733),
+ * extracted directly from `Patch_D2.mpq` (`data/global/excel/MonStats.txt`).
+ */
+export const MONSTER_HCIDX_VELOCITIES: readonly (readonly [number, number])[] = [
+  [3, 3], [4, 4], [4, 4], [5, 5], [5, 5], [1, 3], [1, 4], [1, 4], [1, 5], [1, 5], [6, 6], [6, 6],
+  [5, 5], [5, 5], [7, 7], [4, 4], [4, 4], [5, 5], [6, 6], [5, 5], [5, 5], [6, 6], [6, 6], [8, 8],
+  [4, 4], [4, 4], [5, 5], [5, 5], [3, 3], [5, 5], [5, 5], [6, 6], [6, 6], [7, 7], [0, 0], [0, 0],
+  [0, 0], [0, 0], [5, 5], [6, 6], [6, 6], [7, 7], [8, 8], [5, 5], [6, 8], [6, 10], [7, 12], [8, 12],
+  [7, 12], [7, 12], [7, 13], [7, 13], [7, 14], [5, 5], [6, 6], [7, 7], [9, 9], [8, 8], [4, 4], [4, 4],
+  [5, 5], [5, 5], [6, 6], [3, 3], [3, 3], [4, 4], [4, 4], [5, 5], [4, 4], [4, 4], [4, 4], [4, 4],
+  [4, 4], [4, 4], [4, 10], [5, 12], [5, 12], [6, 14], [10, 10], [8, 8], [8, 8], [8, 8], [8, 8], [5, 10],
+  [6, 11], [7, 12], [8, 13], [5, 5], [6, 6], [7, 7], [8, 8], [4, 4], [5, 5], [5, 5], [6, 6], [6, 6],
+  [3, 3], [3, 3], [3, 3], [3, 3], [3, 3], [2, 2], [2, 2], [3, 3], [4, 4], [5, 5], [3, 3], [3, 3],
+  [3, 3], [3, 3], [4, 4], [4, 4], [5, 5], [5, 5], [6, 12], [6, 12], [6, 12], [6, 12], [15, 15], [15, 15],
+  [15, 15], [15, 15], [6, 6], [7, 7], [8, 8], [8, 9], [8, 11], [3, 3], [3, 3], [3, 3], [3, 3], [6, 6],
+  [7, 7], [7, 7], [8, 8], [9, 9], [7, 7], [8, 8], [9, 9], [10, 10], [12, 12], [6, 6], [7, 7], [8, 8],
+  [9, 9], [10, 10], [2, 2], [4, 4], [1, 1], [2, 2], [3, 3], [5, 5], [8, 8], [0, 0], [4, 4], [3, 3],
+  [8, 8], [7, 7], [4, 4], [7, 7], [4, 4], [5, 6], [5, 8], [6, 9], [7, 10], [4, 4], [5, 6], [5, 8],
+  [6, 10], [7, 12], [4, 4], [4, 4], [5, 5], [5, 5], [5, 5], [3, 3], [3, 3], [3, 3], [3, 3], [2, 2],
+  [4, 4], [4, 4], [5, 5], [5, 5], [6, 6], [5, 5], [3, 3], [4, 4], [6, 6], [8, 8], [1, 1], [1, 1],
+  [1, 1], [1, 1], [1, 1], [2, 2], [2, 2], [2, 2], [4, 4], [3, 3], [2, 2], [4, 4], [3, 3], [4, 7],
+  [4, 4], [4, 4], [0, 0], [0, 0], [0, 0], [0, 0], [4, 4], [10, 15], [6, 6], [7, 7], [8, 8], [9, 9],
+  [10, 10], [4, 4], [4, 4], [5, 5], [5, 5], [5, 5], [3, 3], [3, 3], [4, 4], [4, 4], [4, 4], [1, 1],
+  [0, 0], [2, 2], [4, 4], [4, 4], [4, 4], [4, 4], [4, 4], [6, 8], [6, 9], [6, 11], [6, 6], [6, 6],
+  [6, 6], [6, 6], [8, 8], [6, 6], [2, 2], [2, 2], [2, 2], [9, 9], [10, 10], [11, 11], [5, 5], [0, 0],
+  [2, 2], [2, 2], [2, 2], [2, 2], [10, 16], [2, 2], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0],
+  [2, 2], [2, 2], [8, 8], [6, 8], [2, 2], [5, 5], [8, 8], [7, 11], [8, 8], [0, 0], [4, 4], [4, 4],
+  [5, 5], [5, 5], [6, 6], [7, 7], [8, 8], [9, 9], [10, 10], [1, 1], [4, 4], [4, 4], [4, 4], [4, 4],
+  [4, 4], [8, 8], [9, 9], [9, 9], [10, 10], [12, 6], [3, 2], [10, 16], [3, 2], [2, 2], [7, 7], [7, 7],
+  [7, 7], [8, 10], [9, 11], [10, 12], [10, 16], [10, 16], [10, 16], [6, 12], [7, 12], [8, 12], [6, 7], [7, 7],
+  [8, 7], [4, 4], [4, 4], [5, 5], [5, 5], [6, 6], [2, 2], [5, 5], [5, 5], [0, 0], [0, 0], [0, 0],
+  [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [6, 6], [0, 0], [8, 8], [0, 0], [0, 0],
+  [0, 0], [0, 0], [7, 11], [1, 2], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [6, 12], [8, 12], [10, 12],
+  [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [9, 9], [11, 11], [8, 8], [7, 11],
+  [10, 16], [10, 16], [10, 16], [13, 15], [12, 14], [3, 4], [0, 0], [0, 0], [2, 2], [0, 0], [10, 16], [0, 0],
+  [0, 0], [5, 10], [5, 10], [5, 10], [5, 10], [6, 6], [6, 6], [4, 4], [4, 4], [5, 5], [5, 5], [4, 4],
+  [4, 4], [5, 5], [5, 5], [4, 4], [4, 4], [5, 5], [5, 5], [5, 5], [0, 0], [0, 0], [5, 10], [5, 10],
+  [6, 6], [7, 7], [8, 8], [9, 9], [10, 10], [0, 0], [7, 7], [0, 0], [0, 0], [2, 2], [0, 0], [6, 6],
+  [2, 2], [8, 8], [0, 0], [0, 0], [0, 0], [10, 10], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [10, 20],
+  [5, 10], [5, 10], [6, 6], [6, 6], [6, 6], [7, 7], [7, 7], [7, 7], [5, 9], [6, 6], [6, 6], [6, 6],
+  [0, 0], [0, 0], [0, 0], [0, 0], [1, 5], [1, 5], [2, 5], [2, 5], [3, 5], [3, 7], [3, 8], [4, 9],
+  [5, 10], [6, 11], [5, 8], [6, 6], [7, 7], [7, 7], [1, 1], [1, 1], [1, 1], [7, 10], [7, 10], [7, 10],
+  [7, 10], [7, 10], [7, 10], [7, 10], [7, 10], [10, 10], [10, 10], [10, 10], [10, 10], [10, 10], [10, 10], [10, 10],
+  [10, 10], [10, 10], [11, 11], [12, 12], [13, 13], [14, 14], [7, 7], [8, 8], [9, 9], [10, 10], [12, 12], [4, 4],
+  [4, 4], [5, 5], [5, 5], [6, 6], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0],
+  [7, 7], [7, 7], [7, 7], [7, 7], [7, 7], [0, 0], [0, 0], [0, 0], [0, 0], [3, 3], [3, 3], [3, 3],
+  [3, 3], [3, 3], [9, 9], [9, 9], [9, 9], [9, 9], [9, 9], [3, 3], [3, 3], [1, 1], [2, 2], [3, 3],
+  [0, 0], [0, 0], [0, 0], [0, 0], [2, 2], [0, 0], [5, 14], [5, 14], [0, 0], [0, 0], [7, 7], [2, 2],
+  [0, 0], [4, 4], [4, 4], [5, 5], [5, 5], [6, 6], [4, 7], [5, 14], [5, 14], [5, 14], [5, 14], [5, 14],
+  [10, 10], [10, 10], [10, 10], [6, 6], [6, 6], [12, 12], [6, 6], [6, 6], [6, 6], [6, 6], [6, 6], [8, 10],
+  [8, 10], [8, 10], [8, 10], [8, 10], [2, 2], [10, 12], [10, 16], [6, 6], [8, 14], [8, 14], [0, 0], [0, 0],
+  [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [6, 6], [8, 8], [8, 8], [8, 8], [12, 12], [4, 4],
+  [4, 4], [5, 5], [5, 5], [5, 5], [9, 9], [9, 9], [10, 10], [11, 11], [12, 12], [10, 10], [10, 10], [10, 10],
+  [11, 11], [12, 12], [9, 9], [9, 9], [10, 10], [12, 12], [6, 10], [6, 10], [8, 12], [8, 12], [9, 14], [15, 15],
+  [15, 15], [15, 15], [15, 15], [15, 15], [4, 4], [6, 6], [6, 6], [6, 6], [4, 4], [6, 6], [12, 16], [12, 16],
+  [12, 16], [8, 12], [8, 12], [8, 12], [8, 12], [8, 12], [6, 6], [6, 6], [6, 6], [6, 6], [6, 6], [6, 6],
+  [6, 6], [5, 5], [5, 5], [9, 12], [9, 12], [8, 8], [8, 8], [8, 8], [8, 8], [8, 8], [14, 14], [14, 14],
+  [12, 12], [12, 12], [12, 12], [15, 15], [15, 15], [15, 15], [10, 10], [10, 10], [10, 10], [6, 6], [6, 6], [6, 6],
+  [5, 5], [5, 5], [12, 12], [12, 12], [9, 9], [9, 9], [6, 6], [6, 6], [10, 10], [10, 10], [10, 10], [10, 10],
+  [10, 10], [10, 10], [10, 10], [10, 10], [10, 10], [7, 14], [7, 14], [5, 5], [5, 5], [5, 5], [5, 5], [6, 11],
+  [6, 11], [6, 6], [6, 6], [7, 7], [7, 7], [10, 12], [10, 12], [4, 4], [6, 6], [1, 1], [7, 10], [7, 10],
+  [7, 10], [8, 11], [10, 16], [10, 16], [7, 7], [7, 7], [10, 10], [10, 10], [10, 16], [10, 16], [8, 12], [8, 8],
+  [8, 8], [8, 8], [3, 5], [6, 7], [6, 7], [8, 7], [8, 7], [3, 3], [8, 8], [8, 8], [10, 16], [8, 8],
+  [10, 15], [6, 6], [0, 0], [0, 0], [10, 16], [8, 7], [7, 7], [8, 8], [4, 4], [8, 11], [6, 6], [14, 14],
+  [12, 12], [8, 12], [8, 12], [8, 12], [6, 6], [5, 5], [5, 5], [6, 6], [6, 6], [6, 6], [5, 5], [8, 8],
+  [8, 8], [15, 15],
+]
+
 /**
  * Resolve the visual token and weapon class for a numeric MonStats.txt hcIdx (0..733).
  */

src/common/units/monsters-data.ts

@@ -2038,8 +2038,8 @@ const CANONICAL_113C_MONSTER_OVERRIDES: Readonly<
     attack1: { minDamage: 20, maxDamage: 40, toHit: 70 },
   },
   skeleton1: {
-    velocity: 4,
+    velocity: 3,
-    runVelocity: 4,
+    runVelocity: 3,
     minHp: 61,
     maxHp: 121,
     armour: 100,
@@ -2048,6 +2048,20 @@ const CANONICAL_113C_MONSTER_OVERRIDES: Readonly<
   },
 }
 
+import { MONSTER_HCIDX_TO_ID, MONSTER_HCIDX_VELOCITIES } from './monster-mapping.ts'
+
+const CANONICAL_113C_VELOCITIES_BY_ID: Readonly<Record<string, readonly [number, number]>> = (() => {
+  const out: Record<string, readonly [number, number]> = {}
+  for (let hcIdx = 0; hcIdx < MONSTER_HCIDX_VELOCITIES.length; hcIdx++) {
+    const id = MONSTER_HCIDX_TO_ID[hcIdx]
+    const pair = MONSTER_HCIDX_VELOCITIES[hcIdx]
+    if (id && pair) {
+      out[id] = pair
+    }
+  }
+  return out
+})()
+
 let cachedCanonicalMonsterKinds: Map<string, MonsterKind> | null = null
 
 function getCanonicalMonsterKinds(): Map<string, MonsterKind> {
@@ -2056,11 +2070,14 @@ function getCanonicalMonsterKinds(): Map<string, MonsterKind> {
     const enriched = new Map<string, MonsterKind>()
     for (const [id, kind] of rawKinds) {
       const ov = CANONICAL_113C_MONSTER_OVERRIDES[id]
+      const canonicalSpeed = CANONICAL_113C_VELOCITIES_BY_ID[id.toLowerCase()]
+      const canonicalVel = canonicalSpeed && canonicalSpeed[0] > 0 ? canonicalSpeed[0] : undefined
+      const canonicalRun = canonicalSpeed && canonicalSpeed[1] > 0 ? canonicalSpeed[1] : undefined
       const enrichedKind: MonsterKind = {
         ...kind,
         enabled: kind.killable || !kind.inTown,
-        velocity: ov?.velocity ?? (kind.velocity > 0 ? kind.velocity : 5),
+        velocity: ov?.velocity ?? canonicalVel ?? (kind.velocity > 0 ? kind.velocity : 5),
-        runVelocity: ov?.runVelocity ?? (kind.runVelocity > 0 ? kind.runVelocity : 5),
+        runVelocity: ov?.runVelocity ?? canonicalRun ?? (kind.runVelocity > 0 ? kind.runVelocity : 5),
         minHp: ov?.minHp ?? (kind.minHp > 0 ? kind.minHp : 21),
         maxHp: ov?.maxHp ?? (kind.maxHp > 0 ? kind.maxHp : 61),
         armour: ov?.armour ?? (kind.armour > 0 ? kind.armour : 84),
@@ -2093,7 +2110,12 @@ export const MONSTER_TABLE: ReadonlyMap<string, MonsterKind> & Readonly<Record<s
         return typeof value === 'function' ? value.bind(map) : value
       }
       if (typeof prop === 'string') {
-        return map.get(prop) ?? map.get(prop.toLowerCase())
+        const direct = map.get(prop) ?? map.get(prop.toLowerCase())
+        if (direct !== undefined) return direct
+        if (/^\d+$/.test(prop)) {
+          const id = MONSTER_HCIDX_TO_ID[Number(prop)]
+          if (id) return map.get(id)
+        }
       }
       return undefined
     },
@@ -2104,4 +2126,62 @@ export const MONSTER_TABLE: ReadonlyMap<string, MonsterKind> & Readonly<Record<s
   },
 ) as unknown as ReadonlyMap<string, MonsterKind> & Readonly<Record<string, MonsterKind>>
 
+/**
+ * Look up a canonical 1.13c `MonsterKind` by numeric `MonStats.txt` `hcIdx` (`0..733`).
+ */
+export function getMonsterKindByClassId(classId: number): MonsterKind | undefined {
+  const id = MONSTER_HCIDX_TO_ID[classId]
+  if (!id) return undefined
+  return getCanonicalMonsterKinds().get(id)
+}
 
+/**
+ * Compute D2 1.13c monster movement speed in sub-tiles per second (`D2Common.dll`
+ * `UNITS_GetBaseVelocity` 0x6FDB1170, `UNITS_GetVelocity` 0x6FDB1B60, and `PathMisc.cpp`
+ * `sub_6FDAB8A0` 0x6FDAB8A0).
+ *
+ * - `nBaseVelocity = pMonStatsTxt->nVelocity << 8`
+ * - In `D2Game.dll` (`Monster.cpp:214`), monsters start with base `STAT_VELOCITYPERCENT = 75`.
+ *   When running (`MONMODE_RUN`), `D2Game.dll` (`AiThink.cpp:912`, `MonsterMode.cpp:1925`) adds
+ *   `100 * nRun / nVelocity - 100` to `STAT_VELOCITYPERCENT` and transmits the total in S2C
+ *   `0x67` / `0x68` `nVelocity`.
+ * - `nVelocityPercent = Math.max(25, effectiveVelocityPercent)`
+ * - `dwVelocity = Math.floor((nVelocityPercent * nBaseVelocity) / 100)`
+ * - Per-tick displacement (25 ticks/s): `nVelocityMagnitude = (1024 * dwVelocity) >> 6 = 16 * dwVelocity`
+ *   in `1/65536` sub-tiles/tick -> `(25 * dwVelocity) / 4096` sub-tiles/s.
+ */
+export function computeMonsterMoveSpeedSubTilesPerSec(
+  classId: number,
+  isRun = false,
+  velocityPercent?: number,
+): number {
+  const pair = MONSTER_HCIDX_VELOCITIES[classId]
+  const kind = getMonsterKindByClassId(classId)
+  const baseVelocity =
+    pair && pair[0] > 0
+      ? pair[0]
+      : kind && kind.velocity > 0
+        ? kind.velocity
+        : 5
+  const runVelocity =
+    pair && pair[1] > 0
+      ? pair[1]
+      : kind && kind.runVelocity > 0
+        ? kind.runVelocity
+        : baseVelocity
+
+  let rawPercent: number
+  if (velocityPercent !== undefined && velocityPercent !== 0) {
+    rawPercent = velocityPercent
+  } else if (isRun && baseVelocity > 0 && runVelocity > baseVelocity) {
+    const runBonus = Math.floor((100 * runVelocity) / baseVelocity) - 100
+    rawPercent = 75 + Math.max(0, runBonus)
+  } else {
+    rawPercent = 75
+  }
+
+  const effectivePercent = Math.max(25, rawPercent)
+  const nBaseVelocity = baseVelocity << 8
+  const dwVelocity = Math.floor((effectivePercent * nBaseVelocity) / 100)
+  return (25 * dwVelocity) / 4096
+}

src/netproto/d2gs/s2c/movement.ts

@@ -128,12 +128,21 @@ export function decode0x67NpcMove(pkt: Uint8Array): ServerEvent {
   const moveType = r.u8()
   const targetX = r.u16LE()
   const targetY = r.u16LE()
+  let pathType = 0
+  let velocityPercent = 0
+  if (r.remaining >= 5) {
+    r.u16LE() // unk0x0A
+    pathType = r.u8()
+    velocityPercent = r.i16LE()
+  }
   return {
     type: 'UnitMove',
     unitType: 1,
     id,
     mode: resolveMoveMode(moveType),
     to: { x: targetX, y: targetY },
+    ...(pathType !== 0 ? { pathType } : {}),
+    ...(velocityPercent !== 0 ? { velocityPercent } : {}),
   }
 }
 
@@ -147,6 +156,13 @@ export function decode0x68NpcMoveToTarget(pkt: Uint8Array): ServerEvent {
   const currentY = r.u16LE()
   const targetType = clampUnitType(r.u8())
   const targetId = r.u32LE()
+  let pathType = 0
+  let velocityPercent = 0
+  if (r.remaining >= 5) {
+    r.u16LE() // unk0x0F
+    pathType = r.u8()
+    velocityPercent = r.i16LE()
+  }
   return {
     type: 'UnitMove',
     unitType: 1,
@@ -155,6 +171,8 @@ export function decode0x68NpcMoveToTarget(pkt: Uint8Array): ServerEvent {
     from: { x: currentX, y: currentY },
     to: { x: currentX, y: currentY },
     target: { unitType: targetType, id: targetId },
+    ...(pathType !== 0 ? { pathType } : {}),
+    ...(velocityPercent !== 0 ? { velocityPercent } : {}),
   }
 }
 

src/netproto/domain/server-event.ts

@@ -63,6 +63,8 @@ export type ServerEvent =
       readonly from?: Pt | undefined
       readonly to: Pt
       readonly target?: UnitRef | undefined
+      readonly velocityPercent?: number | undefined
+      readonly pathType?: number | undefined
     }
   | {
       readonly type: 'UnitReassign'

tests/client/unit-facing-motion.test.ts

@@ -15,8 +15,15 @@ import { RemoteEntityInterpolator } from '../../src/client/motion/interpolate.ts
 import type { SubTileWalkabilityGrid } from '../../src/client/motion/pathfind.ts'
 import { LocalMovementPredictor } from '../../src/client/motion/predictor.ts'
 import { HudManager } from '../../src/client/ui/hud-manager.ts'
+import { OnlineSession } from '../../src/client/session/online-session.ts'
 import { ClientWorld } from '../../src/client/world/client-world.ts'
 import { dir64FromPoints, dir64ToClipDirection } from '../../src/common/units/direction.ts'
+import { MONSTER_HCIDX_VELOCITIES } from '../../src/common/units/monster-mapping.ts'
+import {
+  computeMonsterMoveSpeedSubTilesPerSec,
+  getMonsterKindByClassId,
+} from '../../src/common/units/monsters-data.ts'
+import { ByteWriter, decodeD2gsServerPacket } from '../../src/netproto/index.ts'
 import type { ClientCommand } from '../../src/netproto/domain/client-command.ts'
 
 const FRAME_MS = 1000 / 60
@@ -275,3 +282,143 @@ describe('skill-cast facing (ClientWorld)', () => {
     expect(castAt(4990, 4990)).toBe(32) // world −X−Y: screen north
   })
 })
+
+describe('1.13c monster movement velocity & anti-rubber-banding (MonStats.txt + D2Common 0x6FD5D240)', () => {
+  it('populates all 734 MonStats.txt [Velocity, Run] pairs and computes exact 1.13c sub-tile/sec speeds', () => {
+    expect(MONSTER_HCIDX_VELOCITIES.length).toBe(734)
+
+    // Zombies (zombie1..zombie5, hcIdx = 5..9): Velocity = 1 in MonStats.txt ([1,3], [1,4], [1,4], [1,5], [1,5])
+    const expectedZombieRun = [3, 4, 4, 5, 5] as const
+    for (let hcIdx = 5; hcIdx <= 9; hcIdx++) {
+      expect(MONSTER_HCIDX_VELOCITIES[hcIdx]).toEqual([1, expectedZombieRun[hcIdx - 5]])
+      const kind = getMonsterKindByClassId(hcIdx)
+      expect(kind).toBeDefined()
+      expect(kind?.velocity).toBe(1)
+      expect(kind?.runVelocity).toBe(expectedZombieRun[hcIdx - 5])
+      // dwVelocity = floor((75 * 256) / 100) = 192 => 192 * 25 / 4096 = 1.171875 sub-tiles/s
+      expect(computeMonsterMoveSpeedSubTilesPerSec(hcIdx, false, 75)).toBe(1.171875)
+      expect(computeMonsterMoveSpeedSubTilesPerSec(hcIdx, false)).toBe(1.171875)
+    }
+
+    // Skeleton (skeleton1, hcIdx = 0): Velocity = 3, Run = 3
+    // dwVelocity = floor((75 * 768) / 100) = 576 => 576 * 25 / 4096 = 3.515625 sub-tiles/s
+    expect(computeMonsterMoveSpeedSubTilesPerSec(0, false, 75)).toBe(3.515625)
+
+    // Fallen (fallen1, hcIdx = 19): Velocity = 5, Run = 5
+    // Walk (nVelocity = 75): dwVelocity = floor((75 * 1280) / 100) = 960 => 960 * 25 / 4096 = 5.859375 sub-tiles/s
+    expect(computeMonsterMoveSpeedSubTilesPerSec(19, false, 75)).toBe(5.859375)
+    // With explicit run velocityPercent = 155: dwVelocity = floor((155 * 1280) / 100) = 1984 => 12.109375 sub-tiles/s
+    expect(computeMonsterMoveSpeedSubTilesPerSec(19, true, 155)).toBe(12.109375)
+
+    // Corrupt Rogue (corruptrogue2, hcIdx = 44): Velocity = 6, Run = 8
+    // Fallback run without velocityPercent: runBonus = floor(800/6) - 100 = 33 => rawPercent = 108 => dwVelocity = floor((108 * 1536) / 100) = 1658 => 1658 * 25 / 4096 = 10.11962890625
+    expect(computeMonsterMoveSpeedSubTilesPerSec(44, true)).toBeCloseTo((25 * 1658) / 4096, 8)
+
+    // Akara (hcIdx = 148, Velocity = 1) and Kashya (hcIdx = 150, Velocity = 3) from 04-d2gs-idle-60s.d2cap
+    expect(computeMonsterMoveSpeedSubTilesPerSec(148, false, 75)).toBe(1.171875)
+    expect(computeMonsterMoveSpeedSubTilesPerSec(150, false, 75)).toBe(3.515625)
+  })
+
+  it('interpolates Zombie (hcIdx=5) 0x67 NPCMove and 0x68 NPCMoveToTarget at 1.171875 sub-tiles/s without rubber-banding', () => {
+    const session = new OnlineSession()
+
+    // 1. Spawn local player at (5010, 5000) and Zombie (classId=5) at (5000, 5000)
+    session.handleServerEvent({
+      type: 'UnitAssign',
+      isSelf: true,
+      unit: { unitType: 'player', id: 1, classId: 1, name: 'Hero', x: 5010, y: 5000, mode: 1, lifePct: 128 },
+    })
+    session.handleServerEvent({
+      type: 'UnitAssign',
+      unit: { unitType: 'monster', id: 200, classId: 5, x: 5000, y: 5000, mode: 1, lifePct: 128 },
+    })
+
+    // 2. Server sends 0x67 NPCMove for Zombie to walk 3 sub-tiles to (5003, 5000) with nVelocity = 75 (takes 64 ticks = 2560ms)
+    const w67 = new ByteWriter(16)
+    w67.u8(0x67)
+    w67.u32LE(200)
+    w67.u8(0x01) // walk
+    w67.u16LE(5003)
+    w67.u16LE(5000)
+    w67.u16LE(0)
+    w67.u8(2)
+    w67.i16LE(75)
+    w67.u8(0)
+    session.handleServerEvent(decodeD2gsServerPacket(w67.toUint8Array()))
+
+    // Immediately after packet ingestion, Zombie must still be at (5000, 5000), NOT teleported to 5003
+    expect(session.world.getUnit('monster', 200)?.x).toBe(5000)
+    expect(session.interpolator.getEntityState(1, 200)?.x).toBe(5000)
+
+    // 3. Advance 32 ticks (1280ms = half of 2560ms): Zombie must be at 5001.5 (NOT prematurely snapped to 5003 as with old 9 sub-tiles/s!)
+    for (let i = 0; i < 32; i++) {
+      session.tick(40, 1000 + (i + 1) * 40)
+    }
+    expect(session.interpolator.getEntityState(1, 200)?.x).toBeCloseTo(5001.5, 5)
+    expect(session.world.getUnit('monster', 200)?.x).toBeCloseTo(5001.5, 5)
+    expect(session.world.getUnit('monster', 200)?.mode).toBe(2) // still walking (WL)
+
+    // 4. Advance remaining 32 ticks (total 2560ms): Zombie reaches (5003, 5000) exactly when server 0x6D NPCStop arrives
+    for (let i = 32; i < 64; i++) {
+      session.tick(40, 1000 + (i + 1) * 40)
+    }
+    expect(session.interpolator.getEntityState(1, 200)?.x).toBeCloseTo(5003, 5)
+
+    // Server sends 0x6D NPCStop at (5003, 5000) -> zero rubber-band jump!
+    session.handleServerEvent({
+      type: 'UnitMove',
+      unitType: 'monster',
+      id: 200,
+      mode: 'stop',
+      to: { x: 5003, y: 5000 },
+    })
+    expect(session.world.getUnit('monster', 200)?.x).toBeCloseTo(5003, 5)
+
+    // 5. Server sends 0x68 NPCMoveToTarget chasing local player (id=1 at 5010, 5000) from current (5003, 5000) with nVelocity=75
+    const w68 = new ByteWriter(21)
+    w68.u8(0x68)
+    w68.u32LE(200)
+    w68.u8(0x00) // walk in 0x68
+    w68.u16LE(5003)
+    w68.u16LE(5000)
+    w68.u8(0) // targetType = player
+    w68.u32LE(1) // targetId = 1
+    w68.u16LE(0)
+    w68.u8(2)
+    w68.i16LE(75)
+    w68.u8(0)
+    session.handleServerEvent(decodeD2gsServerPacket(w68.toUint8Array()))
+
+    // Step 25 ticks (1000ms): Zombie advances monotonically by 1.171875 sub-tiles to 5004.171875
+    let prevX = session.world.getUnit('monster', 200)!.x
+    for (let i = 0; i < 25; i++) {
+      session.tick(40, 4000 + (i + 1) * 40)
+      const curX = session.world.getUnit('monster', 200)!.x
+      expect(curX).toBeGreaterThanOrEqual(prevX)
+      prevX = curX
+    }
+    expect(prevX).toBeCloseTo(5003 + 1.171875, 4)
+
+    // Server sends next 0x68 re-sync after ~21 ticks (from X = 5004, Y = 5000): Zombie must NOT jump backward or teleport!
+    const w68Next = new ByteWriter(21)
+    w68Next.u8(0x68)
+    w68Next.u32LE(200)
+    w68Next.u8(0x00)
+    w68Next.u16LE(5004)
+    w68Next.u16LE(5000)
+    w68Next.u8(0)
+    w68Next.u32LE(1)
+    w68Next.u16LE(0)
+    w68Next.u8(2)
+    w68Next.i16LE(75)
+    w68Next.u8(0)
+    const xBeforeResync = session.world.getUnit('monster', 200)!.x
+    session.handleServerEvent(decodeD2gsServerPacket(w68Next.toUint8Array()))
+    const xAfterResync = session.world.getUnit('monster', 200)!.x
+    // Drift is ~0.17 sub-tiles (< 1.5 soft-reconcile threshold), so visual position stays at xBeforeResync without rubber-banding!
+    expect(xAfterResync).toBeCloseTo(xBeforeResync, 5)
+
+    session.destroy()
+  })
+})
+

tests/netproto/d2gs-s2c.test.ts

@@ -235,7 +235,31 @@ describe('D2GS S->C 1.13c packet decoders (M1)', () => {
     })
   })
 
-  it('decodes 0x67 NPCMove and 0x68 NPCMoveToTarget walk/run moveType (0x01/0x17 and 0x00/0x18)', () => {
+  it('decodes 0x67 NPCMove and 0x68 NPCMoveToTarget walk/run moveType, pathType, and velocityPercent (1.13c D2PacketDef.h)', () => {
+    // Real 0x67 NPCMove from 04-d2gs-idle-60s.d2cap (Akara id=11 walking to (5313,6294) with pathType=2, nVelocity=75):
+    // 67 0b000000 01 c114 9618 0000 02 4b00 00
+    const akara67 = new Uint8Array([
+      0x67,
+      0x0b, 0x00, 0x00, 0x00, // id = 11
+      0x01,                   // moveType = 0x01 (walk)
+      0xc1, 0x14,             // targetX = 5313
+      0x96, 0x18,             // targetY = 6294
+      0x00, 0x00,             // unk0x0A
+      0x02,                   // pathType = 2 (PATHTYPE_TOWARD)
+      0x4b, 0x00,             // velocityPercent = 75 (0x004b)
+      0x00,                   // unk0x0F
+    ])
+    const ev67 = decodeD2gsServerPacket(akara67)
+    expect(ev67).toEqual({
+      type: 'UnitMove',
+      unitType: 1,
+      id: 11,
+      mode: 'walk',
+      to: { x: 5313, y: 6294 },
+      pathType: 2,
+      velocityPercent: 75,
+    })
+
     const w68Run = new ByteWriter(21)
     w68Run.u8(0x68)
     w68Run.u32LE(88)
@@ -244,13 +268,21 @@ describe('D2GS S->C 1.13c packet decoders (M1)', () => {
     w68Run.u16LE(5200)
     w68Run.u8(0) // targetType = player
     w68Run.u32LE(1) // targetId = 1
-    w68Run.bytes(new Uint8Array(6))
+    w68Run.u16LE(0) // unk0x0F
+    w68Run.u8(2) // pathType = 2
+    w68Run.i16LE(155) // velocityPercent = 155 (e.g. Fallen run: 75 + (100*9/5 - 100) = 155)
+    w68Run.u8(0) // unk0x14
     const ev68 = decodeD2gsServerPacket(w68Run.toUint8Array())
     expect(ev68).toMatchObject({
       type: 'UnitMove',
       unitType: 1,
       id: 88,
       mode: 'run',
+      from: { x: 5100, y: 5200 },
+      target: { unitType: 0, id: 1 },
+      pathType: 2,
+      velocityPercent: 155,
     })
   })
 })
+