Dont play either unless you can get use out of them straight away
When you need to exile your opponents graveyard, the option is there, but if the graveyard isnt immediately relevant, you can cash it in to dig for interaction or a specific card
That puts it in junk Rare territory with Astral Cornucopia (XXX, Astral Cornucopia enters the battlefield with X charge counters on it
Most are desparked Planeswalkers, with some, like Nahiri, Forged in Fury, look set to make a big splash on Commander
Casting Feral Encounter doesn't require any targets
Its a supertype, and the rules still support it , including the world rule that tells the game what to do when more than one world permanent is on the battlefield