#0716 · Gen 6 · Legendary

Xerneas — Best counters

Weaknesses

	Pokémon	Fast move	Charged move	Weather	Score
1	Metagross (Mega)	steelBullet Punch	steelMeteor MashELITE	Snow	10011.5
2	Beedrill (Mega)	poisonPoison Jab	poisonSludge Bomb	Overcast	9711.2
3	Gengar (Mega)	ghostLickELITE	poisonSludge Bomb	Overcast · partial	9410.8
4	Deoxys (Attack)	poisonPoison Jab	electricZap Cannon	Rainy · partial	9010.4
5	Eternatus	poisonPoison Jab	poisonSludge Bomb	Overcast	8910.2
6	Metagross	steelBullet Punch	steelMeteor MashELITE	Snow	869.9
7	Zacian (Crowned)	steelMetal Claw	normalGiga Impact	Partly Cloudy · partial	869.9
8	Naganadel	poisonPoison Jab	poisonSludge Bomb	Overcast	849.7
9	Lucario (Mega)	steelBullet Punch	steelFlash Cannon	Snow	839.5
10	Eternatus (Eternamax)	poisonPoison Jab	poisonSludge Bomb	Overcast	809.2
11	Nihilego	poisonPoison Jab	poisonSludge Bomb	Overcast	809.2
12	Dialga	steelMetal Claw	steelIron Head	Snow	799.1
13	Roserade	poisonPoison Jab	poisonSludge Bomb	Overcast	788.9
14	Kyurem (White)	steelSteel Wing	fireFusion Flare	Clear · partial	778.9
15	Dialga (Origin)	steelMetal Claw	steelIron Head	Snow	778.9
16	Regigigas	normalHidden Power	normalCrush GripELITE	Partly Cloudy	778.8
17	Genesect	steelMetal Claw	steelMagnet Bomb	Snow	768.7
18	Regieleki	normalLock On	electricThunder CageELITE	Rainy · partial	748.6
19	Aggron (Mega)	steelIron Tail	steelHeavy Slam	Snow	738.5
20	Scizor (Mega)	steelBullet Punch	steelIron Head	Snow	738.4

Xerneas is weak to Poison (×1.6), Steel (×1.6).
Watch its Normal/Psychic/Fairy/Bug/Fighting/Electric moves — counters like Beedrill (Mega) and Gengar (Mega) take super-effective damage from them.
Snow weather boosts Steel moves ×1.2 — the best time to battle Xerneas.

Rankings are estimated cycle DPS (attack stat × move damage ÷ cycle time, with STAB and type effectiveness). Not a full battle simulation.