This site has not yet been updated to reflect the changes in Reborn v19.5. It still only reflects the state of the game as of v19.16.
The Pokémon changes its form, alternating between its Full Belly Mode and Hangry Mode after the end of each turn.
There are no Pokémon with this ability. (It's probably a Gen 8 ability that's snuck its way into the database by mistake.)