Mimic

You can still use its optional alternate summoning ability to transform an artifact into the Mimic, and then the Mimic will be banished.

When you summon Mimic, you can choose to summon it normally, or instead you can choose a carriable artifact anywhere in the realm. That artifact is banished, and the Mimic is placed at the artifact's location instead as it transforms. You control the Mimic, and if the artifact did not enter the realm this turn, the Mimic doesn't have Summoning Sickness. It turns out that artifact was a Mimic in disguise all along!