Contingency

Contingency enters the battlefield with your
choice of up to four charge counters on it.
When Contingency enters the battlefield, you may return any number of creatures you control with
total toughness 5 or less to your hand.
Creatures on the battlefield gain {t} pay this
creature's mana value: return it to owner's hand.
At the beginning of your upkeep, put a charge
counter on contingency.
When the fifth charge counter is put on contingency, sacrifice it and destroy all creatures.