Leylea, Time Keeper

Creature spells cost {5} less to cast.
Whenever a creature enters the battlefield, exile it
and put five time counters on it.

{12},{t}, Pay 12 life: Remove all time counters from creatures target player owns in exile.

{12}{12},{t}, Pay 24 life: Remove all time counters
from all creatures in exile. Then, gain control of all creatures.