Sinraffa, of Vast Nations

Vow — At the beginning of each player's upkeep,
that player may vow to not deal damage to
another player until the beginning of their end
step. (When a player breaks their vow they lose 15
life and mil 5 cards. At the beginning of the end step,
if that player upholds their vow, they draw a card and
gain 3 life.)
Other Creatures you control with Vow gain
+1/+1.