The Thing

When The Thing deals combat damage to a player, if it attacked alone and wasn't blocked. Then exile target creature defending player controls and put an assimilation counter on it.

Spawn- Remove an assimilation counter from The Thing and
a card in exile with an assimilation counter: Create a token copy of the exiled card. It also gains The Thing’s abilities.

At the beginning of your end step, put a assimilation counter on The Thing.