Halaster Blackcloak

Cascade
Whenever Halaster Blackcloak enters the battlefield, exile cards from the top of your
library until you exile 3 instant or sorcery cards,
then roll a d6. You may cast X of these spells
without paying their mana cost, where X is half
the result, rounded down. Place all other cards
exiled with this spell on the bottom of your
library in a random order.