Last Day of Summer

When Last Day of Summer enters the battlefield, untap each permanent you control and put a day counter on Last Day of Summer. At your next upkeep, remove that day counter.
If Last Day of Summer has a day counter on it, spells you cast cost {w}{u}{b}{r}{g} less to cast and creatures you control have double strike, flying, menace, haste, and trample. Otherwise, spells you cast cost {5}