Generation Viii
Hunger Switch
The Pokémon changes its form, alternating between its Full Belly Mode and Hangry Mode after the end of each turn.
Detailed Effect
The Pokémon changes its form, alternating between its Full Belly Mode and Hangry Mode after the end of every turn.
Pokémon With Hunger Switch
2 canonical Pokémon forms can have this Ability.

Morpeko Full Belly 
Morpeko Hangry