If I use Counterspell on a The Mimeoplasm that's being cast, are the 2 creatures that have to be removed still removed? Or is this a ETB effect? I ask because of the fuzzy wording on The Mimeoplasm that says as he comes into play first...
The wording clearly says
As The Mimeoplasm enters the battlefield, you may exile two creature cards from graveyards. If you do, it enters the battlefield as a copy of one of those cards with a number of additional +1/+1 counters on it equal to the power of the other card.
So if it's countered, it will not enter the battlefield, the replacement effect won't happen and the creature cards won't be exiled from their graveyards.