Dreaming Spectre

Whenever you gain life for the first time each
turn, you may pay {u}. If you do, draw a card.
Whenever you gain life for the second time each
turn, you may pay {1}{b}. If you do, each
opponent discards two cards.
Whenever you gain life for the third time each
turn, you may pay {2}{w}. If you do, double your
life total.