Temporal Warden

Temporal Shift 1—{2}{w} (You may pay {2}{w} to
exile this card from your hand with 1 shift counter
on it. As long as it has a shift counter, you may cast
it at any time without paying its mana cost. At the
beginning of your upkeep, remove a shift counter.
When there are no shift counters, return it to your
hand.)

As long as you own a card in exile with a shift
counter on it, creatures you control get +1/+1 and
have vigilance.