diff --git a/data/mods/gen4/moves.ts b/data/mods/gen4/moves.ts
index e38589fcf941..821b6ea66463 100644
--- a/data/mods/gen4/moves.ts
+++ b/data/mods/gen4/moves.ts
@@ -47,6 +47,33 @@ export const Moves: import('../../../sim/dex-moves').ModdedMoveDataTable = {
 			},
 		},
 	},
+	assist: {
+		inherit: true,
+		onHit(target) {
+			const moves = [];
+			for (const pokemon of target.side.pokemon) {
+				if (pokemon === target) continue;
+				for (const moveSlot of pokemon.moveSlots) {
+					const moveid = moveSlot.id;
+					const move = this.dex.moves.get(moveid);
+					if (
+						move.flags['noassist'] ||
+						(this.field.pseudoWeather['gravity'] && move.flags['gravity']) ||
+						(target.volatiles['healblock'] && move.flags['heal'])
+					) {
+						continue;
+					}
+					moves.push(moveid);
+				}
+			}
+			let randomMove = '';
+			if (moves.length) randomMove = this.sample(moves);
+			if (!randomMove) {
+				return false;
+			}
+			this.actions.useMove(randomMove, target);
+		},
+	},
 	beatup: {
 		inherit: true,
 		basePower: 10,
@@ -198,6 +225,22 @@ export const Moves: import('../../../sim/dex-moves').ModdedMoveDataTable = {
 			this.add('-start', target, 'typechange', type);
 		},
 	},
+	copycat: {
+		inherit: true,
+		onHit(pokemon) {
+			const move: Move | ActiveMove | null = this.lastMove;
+			if (!move) return;
+
+			if (
+				move.flags['failcopycat'] ||
+				(this.field.pseudoWeather['gravity'] && move.flags['gravity']) ||
+				(pokemon.volatiles['healblock'] && move.flags['heal'])
+			) {
+				return false;
+			}
+			this.actions.useMove(move.id, pokemon);
+		},
+	},
 	cottonspore: {
 		inherit: true,
 		accuracy: 85,
@@ -1007,6 +1050,23 @@ export const Moves: import('../../../sim/dex-moves').ModdedMoveDataTable = {
 	metronome: {
 		inherit: true,
 		flags: {noassist: 1, failcopycat: 1, nosleeptalk: 1, failmimic: 1},
+		onHit(pokemon) {
+			const moves = this.dex.moves.all().filter(move => (
+				(![2, 4].includes(this.gen) || !pokemon.moves.includes(move.id)) &&
+				(!move.isNonstandard || move.isNonstandard === 'Unobtainable') &&
+				move.flags['metronome'] &&
+				!(this.field.pseudoWeather['gravity'] && move.flags['gravity']) &&
+				!(pokemon.volatiles['healblock'] && move.flags['heal'])
+			));
+			let randomMove = '';
+			if (moves.length) {
+				moves.sort((a, b) => a.num - b.num);
+				randomMove = this.sample(moves).id;
+			}
+			if (!randomMove) return false;
+			pokemon.side.lastSelectedMove = this.toID(randomMove);
+			this.actions.useMove(randomMove, pokemon);
+		},
 	},
 	mimic: {
 		inherit: true,
diff --git a/data/moves.ts b/data/moves.ts
index ea281aa1e6b9..1b399f609aaa 100644
--- a/data/moves.ts
+++ b/data/moves.ts
@@ -12187,9 +12187,8 @@ export const Moves: import('../sim/dex-moves').MoveDataTable = {
 		pp: 10,
 		priority: 0,
 		flags: {failencore: 1, nosleeptalk: 1, noassist: 1, failcopycat: 1, failmimic: 1, failinstruct: 1},
-		onHit(target, source, effect) {
+		onHit(pokemon) {
 			const moves = this.dex.moves.all().filter(move => (
-				(![2, 4].includes(this.gen) || !source.moves.includes(move.id)) &&
 				(!move.isNonstandard || move.isNonstandard === 'Unobtainable') &&
 				move.flags['metronome']
 			));
@@ -12199,8 +12198,7 @@ export const Moves: import('../sim/dex-moves').MoveDataTable = {
 				randomMove = this.sample(moves).id;
 			}
 			if (!randomMove) return false;
-			source.side.lastSelectedMove = this.toID(randomMove);
-			this.actions.useMove(randomMove, target);
+			this.actions.useMove(randomMove, pokemon);
 		},
 		callsMove: true,
 		secondary: null,
diff --git a/test/TESTS.md b/test/TESTS.md
index 6c2f32d6bb29..58a89e48bf92 100644
--- a/test/TESTS.md
+++ b/test/TESTS.md
@@ -20,7 +20,7 @@ Check the test/ directory to see if a file already exists for the effect that yo
 		it(`test should start here`, function () {
 
 		});
-	}
+	});
 
 To create the battle, use common.createBattle and pass in two arrays of teams. You can add additional flags as well:
 - gameType: 'doubles', 'triples', 'multi', 'freeforall', etc (tests default to singles)
diff --git a/test/sim/moves/assist.js b/test/sim/moves/assist.js
new file mode 100644
index 000000000000..42c63fb5dd8f
--- /dev/null
+++ b/test/sim/moves/assist.js
@@ -0,0 +1,42 @@
+'use strict';
+
+const assert = require('./../../assert');
+const common = require('./../../common');
+
+let battle;
+
+describe(`[Gen 4] Assist`, function () {
+	afterEach(function () {
+		battle.destroy();
+	});
+
+	it(`should never call moves that would fail under Gravity`, function () {
+		battle = common.gen(4).createBattle([[
+			{species: 'furret', moves: ['assist']},
+			{species: 'smeargle', moves: ['bounce', 'fly', 'highjumpkick', 'splash']},
+			{species: 'smeargle', moves: ['bounce', 'fly', 'highjumpkick', 'splash']},
+			{species: 'smeargle', moves: ['bounce', 'fly', 'highjumpkick', 'splash']},
+			{species: 'smeargle', moves: ['doubleteam', 'fly', 'highjumpkick', 'splash']},
+			{species: 'smeargle', moves: ['bounce', 'fly', 'highjumpkick', 'splash']},
+		], [
+			{species: 'deoxys', moves: ['gravity']},
+		]]);
+		for (let i = 0; i < 5; i++) battle.makeChoices();
+		assert.statStage(battle.p1.active[0], 'evasion', 5);
+	});
+
+	it(`should never call moves that would fail under Heal Block`, function () {
+		battle = common.gen(4).createBattle([[
+			{species: 'furret', moves: ['assist']},
+			{species: 'smeargle', moves: ['recover', 'rest', 'roost', 'wish']},
+			{species: 'smeargle', moves: ['recover', 'rest', 'doubleteam', 'wish']},
+			{species: 'smeargle', moves: ['recover', 'rest', 'roost', 'wish']},
+			{species: 'smeargle', moves: ['recover', 'rest', 'roost', 'wish']},
+			{species: 'smeargle', moves: ['recover', 'rest', 'roost', 'wish']},
+		], [
+			{species: 'latios', moves: ['healblock']},
+		]]);
+		for (let i = 0; i < 5; i++) battle.makeChoices();
+		assert.statStage(battle.p1.active[0], 'evasion', 5);
+	});
+});