Mikaeus, the Unhallowed | Canker Abomination | Evereth, Viceroy of Plunder

Cards

All permanents on the battlefield (
Canker Abomination without a +1/+1 counter on it).

Activate
Evereth by sacrificing
Canker Abomination.
When
Canker Abomination dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
When
Canker Abomination enters the battlefield, it triggers, putting a number of -1/-1 counters on it equal to the number of creatures an opponent controls.
If the opponent had seven or more creatures,
Canker Abomination will die as a state-based action due to having 0 or less toughness. If this occurs, repeat steps 2 through 4 infinitely.
Otherwise, resolve the
Evereth ability, and repeat from step 1.
Cast
Canker Abomination by paying ({2} magic symbol) ({BG} magic symbol) ({BG} magic symbol) .
When
Canker Abomination enters the battlefield, it triggers, putting a number of -1/-1 counters on it equal to the number of creatures an opponent controls.
Canker Abomination dies as a state-based action due to having 0 or less toughness, triggering its undying ability, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
Repeat from step 2.

If you have a way to kill
Evereth and ({1} magic symbol) ({BR} magic symbol) available, you can do so after putting a significant amount of +1/+1 counters on it to deal damage to each opponent using its second ability.

This combo has been estimated to be Exhibition (Bracket 1+).