Little Sister

Shroud, lifelink, Little Sister can't attack.
{t}: Add one mana of any color.
When Little Sister dies, you gain 7 life. If Little
Sister is exiled, draw two cards instead.
When a Big Daddy dies, exile Little Sister, then
create a 7/5 colorless Big Sister token with
deathtouch, first strike, lifelink, riot, reach,
shroud and vigilance.