Beast Boost is an Ability introduced in the seventh generation. It is the signature Ability of the Ultra Beasts. It increases the highest stat of the Pokémon.
In battle, Beast Boost increases the user highest stat (ignoring the HP Stat) by one if the user knocked out a Pokémon in the turn.The ability does not take into account the modifiers caused by status condition,moves or items.However it does take into account the following moves: Power Split, Guard Split. If two or more stat ties the ability will take the one which come first following this order: Attack, Defense, Special Attack, Special Defense, and finally Speed. Beast Boost has no effect outside of battle.