Miirym, Sentinel Wyrm | Worldgorger Dragon

Cards

({3} magic symbol) ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) available.

Cast
Worldgorger Dragon by paying ({3} magic symbol) ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) .
Worldgorger Dragon enters the battlefield, triggering its first ability and
Miirym.
Holding priority, you may activate all mana-producing permanents you control by tapping them, adding at least ({1} magic symbol) .
Resolve the
Miirym trigger, creating a token copy of
Worldgorger Dragon.
The
Worldgorger Dragon token enters the battlefield, exiling all other permanents you control.
The nontoken
Worldgorger Dragon's second ability triggers, returning nothing to the battlefield.
Resolve the nontoken
Worldgorger Dragon's first ability from step 2, exiling all other permanents you control.
The token
Worldgorger Dragon leaves the battlefield, returning all cards exiled with it to the battlefield from exile.
Repeat from step 2 as many times as desired. When you wish to break the loop, repeat the below steps after you've completed step 3.
Resolve the
Worldgorger Dragon trigger, exiling all other permanents you control.
Resolve the
Miirym trigger, creating a token copy of
Worldgorger Dragon.
When the token
Worldgorger Dragon enters the battlefield, its first ability triggers, exiling the nontoken
Worldgorger Dragon.
When the nontoken
Worldgorger Dragon leaves the battlefield, its second ability triggers, returning all cards exiled with it from exile to the battlefield.

This combo has been estimated to be Ruthless (Bracket 4+).