Miirym, Sentinel Wyrm | Mirror Image | Changeling Berserker

Cards

Cast
Changeling Berserker by paying ({3} magic symbol) ({R} magic symbol) .
Changeling Berserker enters the battlefield, triggering its champion ability and
Miirym.
Resolve the
Changeling Berserker trigger, championing
Mirror Image.
Resolve the
Miirym trigger, creating a copy of
Changeling Berserker.
The token
Changeling Berserker enters the battlefield, championing the nontoken
Changeling Berserker.
The nontoken
Changeling Berserker leaves the battlefield, returning
Mirror Image from exile to the battlefield as a copy of the
Changeling Berserker token.
Mirror Image enters the battlefield, triggering its champion ability and
Miirym.
Resolve the
Mirror Image trigger, championing the token
Changeling Berserker.
The token
Changeling Berserker leaves the battlefield, returning the nontoken
Changeling Berserker from exile to the battlefield.
Repeat from step 2.
Resolve all remaining
Miirym triggers, creating infinite nonlegendary copies of
Mirror Image that can copy any creatures you control.