Brother Gats, the Berserker

Whenever Brother Gats, the Berserker attacks,
Brother Gats must be blocked by X creatures if
able, where X is the total amount of life you
have lost this turn before entering your combat
step.
You may cast Brother Gats, the Berserker from
your graveyard by paying {5}{b}{b} and exiling
four other cards from your graveyard rather
than paying its mana cost.