As Ive stated before, I think this is one of the major reasons why weve started to see so many absurd reserved list spikes over the past year or so
That being said, this allowing you to potentially get a crazy amount of stats on board for a short time, and this might be a nice way to enable you to win over the top with some light burn
You just have to control the Aura or Equipment youre targeting as well as the creature youre targeting.
Geralf, the Fleshwright creates a Zombie token when you cast any spell that's not your first spell that turn, Open the Graves creates a Zombie token when a nontoken creatures you control dies, and Cryptbreaker makes a Zombie token by discarding a card and tapping itself
If the ability triggers and the Urn isn't sacrificed (because it left the battlefield or changed controllers, for example), the exiled cards won't be returned to the battlefield