Yidris, Maelstrom Wielder

Trample
Whenever Yidris, Maelstrom Wielder deals
combat damage to a player, as you cast spells
from your hand this turn, they gain cascade.
(When you cast the spell, exile cards from the top of
your library until you exile a nonland card that
costs less. You may cast it without paying its mana
cost. Put the exiled cards on the bottom of your library
in a random order.)