Might doesn't make right, but it does win the fight.

Unleash Fury

Double the power of target creature until end of turn.

Foundations Jumpstart

Starter Commander Decks

Core Set 2021

If an effect instructs you to “double” a creature's power, that creature gets +X/+0, where X is its power as that effect begins to apply. If its power is negative, instead it gets -X/-0 where X is how far below 0 its power is. The value of X won't change if another effect alters the creature's power later in the turn.