Xyst of Chaotic Deeds

At the beginning of your precombat main phase
you may sacrifice a nontoken creature. If you do, target opponent sacrifices X permanents they control, where X is half the number of Shrines
you control, rounded down.
Beneath this ancient portico, malicious rituals of
unknown origin are performed, bringing forth
nightmare and nefarious creatures of unending chaos.
This dark and evil magic twists the land itself, irreparably damaging the surrounding environment.