I generally set exiled cards aside, face up, farther out than my graveyard, or tilted 90 degrees underneath my graveyard
There was a point where the card was literally everywhere, as Izzet Murktide decks and beyond utilized full playsets
Over the years weve learned that cheating mana or making freer spells is never a good idea
This may be a slight nod to cEDH on my part, but I also think that being a staple of the highest-powered Commander variant should count when evaluating a card
If there are no creature cards exiled with Assimilation Aegis when its second ability resolves, the creature Assimilation Aegis is attached to won't become a copy of anything else
I want one for my collection, and I suspect that you might want one for yours