Mantha, Time Delver

Omen 1 - {1}{w}{u} (Rather than cast this card
from your hand, pay {1}{w}{u} and exile it with one
time counter on it. When the last counter is removed,
cast it without paying its mana cost.)
Whenever a time counter is removed from
Mantha, Time Delver remove a time counter
from each other card you own in exile.
Counter target spell you control: Return Mantha,
Time Delver to your hand.