The Bloodsky Massacre (207)

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Create a 2/3 red Demon Berserker creature token with menace.
II — Whenever a Berserker attacks this turn, you draw a card and you lose 1 life.
III — Add for each Berserker you control. Until end of turn, you don't lose this mana as steps and phases end.