diff --git a/frontend/src/components/FightViewer.vue b/frontend/src/components/FightViewer.vue
index b67e5d7..4da191b 100644
--- a/frontend/src/components/FightViewer.vue
+++ b/frontend/src/components/FightViewer.vue
@@ -13,6 +13,7 @@ import {
   sfxRandomComedy, sfxRandomFail, sfxVineBoom, sfxEmotionalDamage,
 } from '../game/audio'
 import { isKokoroLoading, getKokoroProgress } from '../game/tts'
+import { isPerfMode, setPerfMode } from '../game/fight/config'
 
 interface Round {
   roundNumber: number
@@ -73,6 +74,7 @@ const hitTextY = ref(30)
 const glitching = ref(false)
 const soundOn = ref(true)
 const insanityMode = ref(false)
+const perfMode = ref(false)
 
 // Zap the winner
 const zapSent = ref(false)
@@ -155,6 +157,12 @@ function toggleInsanity() {
   }
 }
 
+perfMode.value = isPerfMode()
+function togglePerfMode() {
+  perfMode.value = !perfMode.value
+  setPerfMode(perfMode.value)
+}
+
 // Staggered log
 const logItems = ref<{ type: string; round: number; text: string; color: string }[]>([])
 
@@ -808,6 +816,16 @@ async function _doReplay() {
             <path d="M11 5L6 9H2v6h4l5 4V5z"/><line x1="23" y1="9" x2="17" y2="15"/><line x1="17" y1="9" x2="23" y2="15"/>
           </svg>
         </button>
+        <button
+          class="w-8 h-8 flex items-center justify-center border text-[9px] font-pixel tracking-wider transition-all"
+          :class="perfMode
+            ? 'border-neon-green/70 text-neon-green bg-neon-green/10'
+            : 'border-border/50 text-text-muted hover:text-neon-green hover:border-neon-green/50'"
+          :title="perfMode ? 'Performance mode ON (fewer particles)' : 'Performance mode OFF'"
+          @click="togglePerfMode"
+        >
+          {{ perfMode ? 'LO' : 'HI' }}
+        </button>
         <button
           v-if="isReplaying"
           class="h-8 px-2 flex items-center justify-center border text-[9px] font-pixel tracking-wider transition-all"
diff --git a/frontend/src/game/FightScene.ts b/frontend/src/game/FightScene.ts
index 972af92..320c5fe 100644
--- a/frontend/src/game/FightScene.ts
+++ b/frontend/src/game/FightScene.ts
@@ -8,7 +8,7 @@ import { ARENA_THEMES, spriteAnims, CHALLENGE_THEMED, TIER_ULTIMATES, CREATOR_MO
 import {
   CREATOR_ULTIMATE_CHANCE, CREATOR_THEMED_MOVE_RATIO,
   CRIT_THEMED_RATIO, CHOREOGRAPHY_THEMED_RATIO, CHOREOGRAPHY_GENERIC_CUTOFF,
-  TIER_ULTIMATE_CHANCES,
+  TIER_ULTIMATE_CHANCES, isPerfMode, perfParticles,
 } from './fight/config'
 import { spawnSparks as _spawnSparks, spawnBulletHoles as _spawnBulletHoles, spawnExhaust as _spawnExhaust } from './fight/particles'
 import { glitchRGB as _glitchRGB, scanlineGlitch as _scanlineGlitch, vhsTracking as _vhsTracking, dimensionalShift as _dimensionalShift } from './fight/effects'
@@ -361,9 +361,10 @@ export async function createFightScene(config: FightSceneConfig) {
 
   // Hyperspeed lines — converging toward a point
   function hyperSpeedLines(targetX: number, targetY: number, duration: number = 0.3) {
+    const lineCount = isPerfMode() ? 6 : 16
     const lines: GameObj[] = []
-    for (let i = 0; i < 16; i++) {
-      const angle = (i / 16) * Math.PI * 2
+    for (let i = 0; i < lineCount; i++) {
+      const angle = (i / lineCount) * Math.PI * 2
       const dist = 300 + Math.random() * 200
       const sx = targetX + Math.cos(angle) * dist
       const sy = targetY + Math.sin(angle) * dist
@@ -415,7 +416,8 @@ export async function createFightScene(config: FightSceneConfig) {
   // Spawn afterimages: trailing ghost sprites behind a moving fighter
   function spawnAfterimages(fighter: Fighter, count: number = 3) {
     if (!fighter?.exists()) return
-    for (let i = 0; i < count; i++) {
+    const n = isPerfMode() ? Math.max(1, Math.round(count * 0.5)) : count
+    for (let i = 0; i < n; i++) {
       const ghost = k.add([
         k.rect(FRAME_SIZE * Math.abs(fighter.scale.x), FRAME_SIZE * Math.abs(fighter.scale.y)),
         k.pos(fighter.pos.x - i * 8 * Math.sign(fighter.scale.x), fighter.pos.y),
@@ -456,7 +458,8 @@ export async function createFightScene(config: FightSceneConfig) {
     const acc = theme.accent
 
     // Parallax stars/particles in the sky
-    for (let i = 0; i < 40; i++) {
+    const starCount = isPerfMode() ? 15 : 40
+    for (let i = 0; i < starCount; i++) {
       const star = k.add([
         k.rect(1 + Math.random() * 2, 1 + Math.random() * 2),
         k.pos(Math.random() * W, Math.random() * (GROUND_Y - 20)),
@@ -472,21 +475,25 @@ export async function createFightScene(config: FightSceneConfig) {
     }
 
     if (a === 'datacenter' || a === 'localhost') {
+      const perf = isPerfMode()
       // City skyline silhouette behind the racks
-      const buildingHeights = [0.55, 0.4, 0.65, 0.35, 0.7, 0.45, 0.6, 0.5, 0.72, 0.38, 0.58, 0.42]
+      const buildingHeights = perf
+        ? [0.55, 0.65, 0.7, 0.6, 0.72, 0.58]
+        : [0.55, 0.4, 0.65, 0.35, 0.7, 0.45, 0.6, 0.5, 0.72, 0.38, 0.58, 0.42]
       for (let i = 0; i < buildingHeights.length; i++) {
         const bw = W / buildingHeights.length + 4
         const bh = GROUND_Y * buildingHeights[i]
         const bx = i * (W / buildingHeights.length)
         k.add([k.rect(bw, bh), k.pos(bx, GROUND_Y - bh), k.color(safeColor(k, '#060610')), k.opacity(0.5), k.z(0)])
+        const winStep = perf ? 14 : 7
         for (let wy = 0; wy < bh - 10; wy += 8) {
-          for (let wx = 4; wx < bw - 6; wx += 7) {
+          for (let wx = 4; wx < bw - 6; wx += winStep) {
             const win = k.add([
               k.rect(3, 3), k.pos(bx + wx, GROUND_Y - bh + 6 + wy),
               k.color(safeColor(k, Math.random() > 0.4 ? '#223355' : '#ffcc44')),
               k.opacity(0.15 + Math.random() * 0.2), k.z(0),
             ])
-            if (Math.random() < 0.15) {
+            if (!perf && Math.random() < 0.15) {
               const blink = 0.03 + Math.random() * 0.06
               win.onUpdate(() => { win.opacity = Math.random() > blink ? win.opacity : (Math.random() > 0.5 ? 0.3 : 0.05) })
             }
@@ -494,11 +501,13 @@ export async function createFightScene(config: FightSceneConfig) {
         }
       }
       // Server rack wall
-      for (let row = 0; row < 4; row++) {
-        for (let col = 0; col < 10; col++) {
-          const lx = 15 + col * (W / 10)
+      const rackRows = perf ? 2 : 4
+      const rackCols = perf ? 5 : 10
+      for (let row = 0; row < rackRows; row++) {
+        for (let col = 0; col < rackCols; col++) {
+          const lx = 15 + col * (W / rackCols)
           const ly = 15 + row * 55
-          const rackW = W / 10 - 8
+          const rackW = W / rackCols - 8
           const rackH = 48
           k.add([k.rect(rackW, rackH), k.pos(lx, ly), k.color(safeColor(k, '#06060f')), k.opacity(0.6), k.z(1)])
           k.add([k.rect(rackW, 1), k.pos(lx, ly), k.color(safeColor(k, '#1a1a3a')), k.opacity(0.4), k.z(1)])
@@ -507,21 +516,23 @@ export async function createFightScene(config: FightSceneConfig) {
           for (let s = 0; s < 5; s++) {
             k.add([k.rect(rackW - 6, 1), k.pos(lx + 3, ly + 8 + s * 8), k.color(safeColor(k, '#111122')), k.opacity(0.5), k.z(1)])
           }
-          for (let led = 0; led < 3; led++) {
-            const ledEl = k.add([
-              k.rect(2, 2), k.pos(lx + 4 + led * 6, ly + 4),
-              k.color(safeColor(k, Math.random() > 0.3 ? '#00ff41' : '#ff2d2d')),
-              k.opacity(0.7), k.z(2),
-            ])
-            const blinkRate = 0.02 + Math.random() * 0.08
-            ledEl.onUpdate(() => { ledEl.opacity = Math.random() > blinkRate ? 0.7 : 0.15 })
-          }
-          if (Math.random() < 0.4) {
-            const actLed = k.add([
-              k.rect(2, 2), k.pos(lx + rackW - 8, ly + 4),
-              k.color(safeColor(k, '#ffaa00')), k.opacity(0.6), k.z(2),
-            ])
-            actLed.onUpdate(() => { actLed.opacity = Math.random() > 0.5 ? 0.7 : 0.2 })
+          if (!perf) {
+            for (let led = 0; led < 3; led++) {
+              const ledEl = k.add([
+                k.rect(2, 2), k.pos(lx + 4 + led * 6, ly + 4),
+                k.color(safeColor(k, Math.random() > 0.3 ? '#00ff41' : '#ff2d2d')),
+                k.opacity(0.7), k.z(2),
+              ])
+              const blinkRate = 0.02 + Math.random() * 0.08
+              ledEl.onUpdate(() => { ledEl.opacity = Math.random() > blinkRate ? 0.7 : 0.15 })
+            }
+            if (Math.random() < 0.4) {
+              const actLed = k.add([
+                k.rect(2, 2), k.pos(lx + rackW - 8, ly + 4),
+                k.color(safeColor(k, '#ffaa00')), k.opacity(0.6), k.z(2),
+              ])
+              actLed.onUpdate(() => { actLed.opacity = Math.random() > 0.5 ? 0.7 : 0.2 })
+            }
           }
         }
       }
@@ -536,7 +547,8 @@ export async function createFightScene(config: FightSceneConfig) {
 
     } else if (a === 'gpu_graveyard') {
       // Floating circuit board fragments
-      for (let i = 0; i < 16; i++) {
+      const chipCount = isPerfMode() ? 6 : 16
+      for (let i = 0; i < chipCount; i++) {
         const cx = Math.random() * W
         const cy = 20 + Math.random() * (GROUND_Y - 60)
         const cw = 15 + Math.random() * 25
diff --git a/frontend/src/game/fight/config.ts b/frontend/src/game/fight/config.ts
index 828ce49..6bb8d04 100644
--- a/frontend/src/game/fight/config.ts
+++ b/frontend/src/game/fight/config.ts
@@ -2,6 +2,38 @@
 // Gameplay constants — all tunable magic numbers in one place
 // ═══════════════════════════════════════════════════════════════
 
+// --- Performance mode ---
+const PERF_KEY = 'bf_perf_mode'
+
+function detectLowEnd(): boolean {
+  if (typeof navigator === 'undefined') return false
+  const cores = navigator.hardwareConcurrency || 4
+  const mobile = navigator.maxTouchPoints > 0
+  return cores < 4 || mobile
+}
+
+function loadPerfPref(): boolean | null {
+  try {
+    const v = localStorage.getItem(PERF_KEY)
+    if (v === '1') return true
+    if (v === '0') return false
+  } catch {}
+  return null
+}
+
+let _perfMode = loadPerfPref() ?? detectLowEnd()
+
+export function isPerfMode(): boolean { return _perfMode }
+export function setPerfMode(on: boolean): void {
+  _perfMode = on
+  try { localStorage.setItem(PERF_KEY, on ? '1' : '0') } catch {}
+}
+
+/** Scale a particle count down in performance mode (40%) */
+export function perfParticles(count: number): number {
+  return _perfMode ? Math.max(1, Math.round(count * 0.4)) : count
+}
+
 // --- Choreography selection probabilities ---
 export const CREATOR_ULTIMATE_CHANCE = 0.5          // Creator ultimate chance (non-crit); 1.0 on crits
 export const CREATOR_THEMED_MOVE_RATIO = 0.6        // Creator uses creator-themed moves 60% of the time
diff --git a/frontend/src/game/fight/particles.ts b/frontend/src/game/fight/particles.ts
index be18d0d..ffb313c 100644
--- a/frontend/src/game/fight/particles.ts
+++ b/frontend/src/game/fight/particles.ts
@@ -1,9 +1,11 @@
 import type { FightContext } from './types'
+import { perfParticles, isPerfMode } from './config'
 
 export function spawnSparks(ctx: FightContext, x: number, y: number, count: number, color: string): void {
   const { k, safeColor } = ctx
+  const n = perfParticles(count)
   const intense = count > 8
-  for (let i = 0; i < count; i++) {
+  for (let i = 0; i < n; i++) {
     const angle = Math.random() * Math.PI * 2
     const speed = (intense ? 150 : 100) + Math.random() * (intense ? 400 : 300)
     const size = (intense ? 3 : 2) + Math.random() * (intense ? 6 : 4)
@@ -31,7 +33,8 @@ export function spawnSparks(ctx: FightContext, x: number, y: number, count: numb
 
 export function spawnBulletHoles(ctx: FightContext, x: number, y: number, count: number): void {
   const { k, safeColor, trackedTimeout, trackedInterval, clearTracked } = ctx
-  for (let i = 0; i < count; i++) {
+  const n = perfParticles(count)
+  for (let i = 0; i < n; i++) {
     const hole = k.add([
       k.circle(3 + Math.random() * 3),
       k.pos(x + (Math.random() - 0.5) * 40, y + (Math.random() - 0.5) * 60),
@@ -53,7 +56,8 @@ export function spawnExhaust(ctx: FightContext, x: number, y: number, duration:
   const endTime = performance.now() + duration * 1000
   const interval = trackedInterval(() => {
     if (performance.now() > endTime) { clearTracked(interval); return }
-    for (let i = 0; i < 3; i++) {
+    const exhaustCount = isPerfMode() ? 1 : 3
+    for (let i = 0; i < exhaustCount; i++) {
       const p = k.add([
         k.circle(3 + Math.random() * 5),
         k.pos(x + (Math.random() - 0.5) * 15, y),