Arkangel

Trample, City's Haven
Whenever you sacrifice a creature Arkangel gets
+1/+1 until end of turn.
Sacrifice a creature:Add {b}
Sacrifice 4 creatures:Draw a card
You don't lose unspent black mana as steps and
phases end.
At the beginning of your end step lose all
unspent mana and deal X damage to target
opponent where X is the amount of black
mana lost this way.