works, needs some testing

src/data/ability.ts

@@ -715,7 +715,7 @@ export class PostDefendContactApplyStatusEffectAbAttr extends PostDefendAbAttr {
   applyPostDefend(pokemon: Pokemon, passive: boolean, attacker: Pokemon, move: PokemonMove, hitResult: HitResult, args: any[]): boolean {
     if (move.getMove().checkFlag(MoveFlags.MAKES_CONTACT, attacker, pokemon) && !attacker.status && (this.chance === -1 || pokemon.randSeedInt(100) < this.chance)) {
       const effect = this.effects.length === 1 ? this.effects[0] : this.effects[pokemon.randSeedInt(this.effects.length)];
-      return attacker.trySetStatus(effect, true);
+      return attacker.trySetStatus(effect, true, pokemon);
     }
 
     return false;
@@ -1759,6 +1759,24 @@ export class StatusEffectImmunityAbAttr extends PreSetStatusAbAttr {
   }
 }
 
+export class PostSetStatusAbAttr extends AbAttr {
+  applyPostSetStatus(pokemon: Pokemon, source: Pokemon = null, passive: boolean, effect: StatusEffect, args: any[]): boolean | Promise<boolean> {
+    return false;
+  }
+}
+
+/**
+ * If another Pokemon burns, paralyzes, poisons, or badly poisons this Pokemon, that Pokemon receives the same non-volatile status condition.
+ */
+export class StatusSyncAbAttr extends PostSetStatusAbAttr {
+  applyPostSetStatus(pokemon: Pokemon, source: Pokemon = null, passive: boolean, effect: StatusEffect, args: any[]): boolean | Promise<boolean> {
+    if (source && [StatusEffect.BURN, StatusEffect.PARALYSIS, StatusEffect.POISON, StatusEffect.TOXIC].includes(effect)) {
+      return source.trySetStatus(effect, true);
+    }
+    return false;
+  }
+}
+
 export class PreApplyBattlerTagAbAttr extends AbAttr {
   applyPreApplyBattlerTag(pokemon: Pokemon, passive: boolean, tag: BattlerTag, cancelled: Utils.BooleanHolder, args: any[]): boolean | Promise<boolean> {
     return false;
@@ -2804,6 +2822,11 @@ export function applyPreSetStatusAbAttrs(attrType: { new(...args: any[]): PreSet
   return applyAbAttrsInternal<PreSetStatusAbAttr>(attrType, pokemon, (attr, passive) => attr.applyPreSetStatus(pokemon, passive, effect, cancelled, args), args, false, false, !simulated);
 }
 
+export function applyPostSetStatusAbAttrs(attrType: { new(...args: any[]): PostSetStatusAbAttr },
+  pokemon: Pokemon, effect: StatusEffect, source?: Pokemon, ...args: any[]): Promise<void> {
+  return applyAbAttrsInternal<PostSetStatusAbAttr>(attrType, pokemon, (attr, passive) => attr.applyPostSetStatus(pokemon, source, passive, effect, args), args);
+}
+
 export function applyPreApplyBattlerTagAbAttrs(attrType: { new(...args: any[]): PreApplyBattlerTagAbAttr },
   pokemon: Pokemon, tag: BattlerTag, cancelled: Utils.BooleanHolder, ...args: any[]): Promise<void> {
   return applyAbAttrsInternal<PreApplyBattlerTagAbAttr>(attrType, pokemon, (attr, passive) => attr.applyPreApplyBattlerTag(pokemon, passive, tag, cancelled, args), args);
@@ -2945,8 +2968,8 @@ export function initAbilities() {
     new Ability(Abilities.EFFECT_SPORE, 3)
       .attr(EffectSporeAbAttr),
     new Ability(Abilities.SYNCHRONIZE, 3)
-      .attr(SyncEncounterNatureAbAttr)
+      .attr(StatusSyncAbAttr)
-      .unimplemented(),
+      .attr(SyncEncounterNatureAbAttr),
     new Ability(Abilities.CLEAR_BODY, 3)
       .attr(ProtectStatAbAttr)
       .ignorable(),

src/data/move.ts

@@ -1156,7 +1156,7 @@ export class StatusEffectAttr extends MoveEffectAttr {
           return false;
       }
       if (!pokemon.status || (pokemon.status.effect === this.effect && move.chance < 0))
-        return pokemon.trySetStatus(this.effect, true, this.cureTurn);
+        return pokemon.trySetStatus(this.effect, true, user, this.cureTurn);
     }
     return false;
   }
@@ -1197,7 +1197,7 @@ export class PsychoShiftEffectAttr extends MoveEffectAttr {
       return false;
     }
     if (!target.status || (target.status.effect === statusToApply && move.chance < 0)) {
-      var statusAfflictResult = target.trySetStatus(statusToApply, true);
+      var statusAfflictResult = target.trySetStatus(statusToApply, true, user);
       if (statusAfflictResult) {
         user.scene.queueMessage(getPokemonMessage(user, getStatusEffectHealText(user.status.effect)));
         user.resetStatus();

src/field/pokemon.ts

@@ -27,7 +27,7 @@ import { TempBattleStat } from '../data/temp-battle-stat';
 import { ArenaTagSide, WeakenMoveScreenTag, WeakenMoveTypeTag } from '../data/arena-tag';
 import { ArenaTagType } from "../data/enums/arena-tag-type";
 import { Biome } from "../data/enums/biome";
-import { Ability, AbAttr, BattleStatMultiplierAbAttr, BlockCritAbAttr, BonusCritAbAttr, BypassBurnDamageReductionAbAttr, FieldPriorityMoveImmunityAbAttr, FieldVariableMovePowerAbAttr, IgnoreOpponentStatChangesAbAttr, MoveImmunityAbAttr, MoveTypeChangeAttr, NonSuperEffectiveImmunityAbAttr, PreApplyBattlerTagAbAttr, PreDefendFullHpEndureAbAttr, ReceivedMoveDamageMultiplierAbAttr, ReduceStatusEffectDurationAbAttr, StabBoostAbAttr, StatusEffectImmunityAbAttr, TypeImmunityAbAttr, VariableMovePowerAbAttr, VariableMoveTypeAbAttr, WeightMultiplierAbAttr, allAbilities, applyAbAttrs, applyBattleStatMultiplierAbAttrs, applyPostDefendAbAttrs, applyPreApplyBattlerTagAbAttrs, applyPreAttackAbAttrs, applyPreDefendAbAttrs, applyPreSetStatusAbAttrs, UnsuppressableAbilityAbAttr, SuppressFieldAbilitiesAbAttr, NoFusionAbilityAbAttr, MultCritAbAttr, IgnoreTypeImmunityAbAttr, DamageBoostAbAttr } from '../data/ability';
+import { Ability, AbAttr, BattleStatMultiplierAbAttr, BlockCritAbAttr, BonusCritAbAttr, BypassBurnDamageReductionAbAttr, FieldPriorityMoveImmunityAbAttr, FieldVariableMovePowerAbAttr, IgnoreOpponentStatChangesAbAttr, MoveImmunityAbAttr, MoveTypeChangeAttr, NonSuperEffectiveImmunityAbAttr, PreApplyBattlerTagAbAttr, PreDefendFullHpEndureAbAttr, ReceivedMoveDamageMultiplierAbAttr, ReduceStatusEffectDurationAbAttr, StabBoostAbAttr, StatusEffectImmunityAbAttr, TypeImmunityAbAttr, VariableMovePowerAbAttr, VariableMoveTypeAbAttr, WeightMultiplierAbAttr, allAbilities, applyAbAttrs, applyBattleStatMultiplierAbAttrs, applyPostDefendAbAttrs, applyPreApplyBattlerTagAbAttrs, applyPreAttackAbAttrs, applyPreDefendAbAttrs, applyPreSetStatusAbAttrs, UnsuppressableAbilityAbAttr, SuppressFieldAbilitiesAbAttr, NoFusionAbilityAbAttr, MultCritAbAttr, IgnoreTypeImmunityAbAttr, DamageBoostAbAttr, applyPostSetStatusAbAttrs, PostSetStatusAbAttr } from '../data/ability';
 import { Abilities } from "#app/data/enums/abilities";
 import PokemonData from '../system/pokemon-data';
 import Battle, { BattlerIndex } from '../battle';
@@ -2065,12 +2065,12 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
     return true;
   }
 
-  trySetStatus(effect: StatusEffect, asPhase: boolean = false, cureTurn: integer = 0, sourceText: string = null): boolean {
+  trySetStatus(effect: StatusEffect, asPhase: boolean = false, source?: Pokemon, cureTurn: integer = 0, sourceText: string = null): boolean {
     if (!this.canSetStatus(effect, asPhase))
       return false;
 
     if (asPhase) {
-      this.scene.unshiftPhase(new ObtainStatusEffectPhase(this.scene, this.getBattlerIndex(), effect, cureTurn, sourceText));
+      this.scene.unshiftPhase(new ObtainStatusEffectPhase(this.scene, this.getBattlerIndex(), effect, cureTurn, sourceText, source));
       return true;
     }
 
@@ -2102,6 +2102,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
 
     if (effect !== StatusEffect.FAINT)
       this.scene.triggerPokemonFormChange(this, SpeciesFormChangeStatusEffectTrigger, true);
+      applyPostSetStatusAbAttrs(PostSetStatusAbAttr, this, effect, source);
 
     return true;
   }

src/phases.ts

@@ -2931,19 +2931,21 @@ export class ObtainStatusEffectPhase extends PokemonPhase {
   private statusEffect: StatusEffect;
   private cureTurn: integer;
   private sourceText: string;
+  private source: Pokemon;
 
-  constructor(scene: BattleScene, battlerIndex: BattlerIndex, statusEffect: StatusEffect, cureTurn?: integer, sourceText?: string) {
+  constructor(scene: BattleScene, battlerIndex: BattlerIndex, statusEffect: StatusEffect, cureTurn?: integer, sourceText?: string, source?: Pokemon) {
     super(scene, battlerIndex);
 
     this.statusEffect = statusEffect;
     this.cureTurn = cureTurn;
     this.sourceText = sourceText;
+    this.source = source;
   }
 
   start() {
     const pokemon = this.getPokemon();
     if (!pokemon.status) {
-      if (pokemon.trySetStatus(this.statusEffect)) {
+      if (pokemon.trySetStatus(this.statusEffect, false, this.source)) {
         if (this.cureTurn)
           pokemon.status.cureTurn = this.cureTurn;
         pokemon.updateInfo(true);