Assimilation Aegis

If you somehow exile a noncreature card with Assimilation Aegis's first ability (possibly because it was a copy of a creature while on the battlefield), you can't choose to have the creature Assimilation Aegis is attached to become a copy of that card when Assimilation Aegis's second ability resolves.

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. It will remain just as it was.

Any non-copy effects that applied to the creature Assimilation Aegis is attached to before it becomes a copy of another card will continue to apply once it becomes a copy. The same is true of any counters that are on that creature.