Khumsyum, Agony Unceasing

Khumsyum, Agony Unceasing is all colors.
Whenever a creature card enters the graveyard or exile from anywhere, choose a color not in that card's colors. Until end of turn, spells you cast of that color or that target a permanent of that color cost {1} less to cast. Then if you chose— white: untap target permanent; blue: draw a card, then discard a card; black: you lose 1 life and draw a card; red: you may disc