Kruul-karak demon general

Whenever a demon you control attacks exile the top X cards of your library. You may cast those cards this turn, with their cost reduced by X.
X is the number of demons you control.
Demon/devil spells you cast have demon/devil
cascade.(after casting a demon/devil spell, exile the
top cards of your library until you exile a demon/devil
card with mana cost less then the played card. Put that
card onto the battlefield and put the exiled cards on the bottom of your library.)