Swarm

Swarm increases the power of Bug-type moves by 50% (1.5×) when the ability-bearer's HP falls below a third of its maximum (known in-game as in a pinch).

Game descriptions

Ruby, Sapphire, FireRed, LeafGreen, Emerald:Ups BUG moves in a pinch.
Diamond, Pearl, Platinum, HeartGold, SoulSilver:Powers up Bug-type moves in a pinch.
Black, White, Black 2, White 2:Powers up Bug-type moves in a pinch.
X, Y, O.Ruby, A.Sapphire:Powers up Bug-type moves when the Pokémon is in trouble.
Sun, Moon, Ultra Sun, Ultra Moon:Powers up Bug-type moves when the Pokémon’s HP is low.
Sword, Shield, B.Diamond, S.Pearl:Powers up Bug-type moves when the Pokémon’s HP is low.
Scarlet, Violet:Powers up Bug-type moves when the Pokémon’s HP is low.

Swarm

Game descriptions

Pokémon with this ability (31)