Gatha, Tolarian Renegade

When Gatha enters the battlefield, you may exile
the top four cards of your library. Until the end
of your next turn, you may play those cards.
Whenever you cast an instant or sorcery spell
from your library, put a time counter on a card
exiled by Gatha.
You may play cards in exile with time counters
on them and without paying their mana cost.