Inner Focus

Inner Focus prevents the Pokémon from flinching, for example when attacked by a move like Headbutt.

Game descriptions

Ruby, Sapphire, FireRed, LeafGreen, Emerald:Prevents flinching.
Diamond, Pearl, Platinum, HeartGold, SoulSilver:The Pokémon is protected from flinching.
Black, White, Black 2, White 2:The Pokémon is protected from flinching.
X, Y, O.Ruby, A.Sapphire:Protects the Pokémon from flinching.
Sun, Moon, Ultra Sun, Ultra Moon:The Pokémon’s intensely focused, and that protects the Pokémon from flinching.
Sword, Shield, B.Diamond, S.Pearl:The Pokémon’s intensely focused, and that protects the Pokémon from flinching.
Scarlet, Violet:The Pokémon’s intense focus prevents it from flinching or being affected by Intimidate.