Mikaeus, the Unhallowed + Workhorse + Crovax, Ascendant Hero

Mikaeus, the Unhallowed

Workhorse

Crovax, Ascendant Hero

How it works

1. Activate Workhorse by removing a +1/+1 counter from it, adding C.
2. Repeat step 1 until Workhorse does not have any +1/+1 counters on it.
3. Workhorse dies as a state-based action due to having zero toughness.
4. Workhorse's undying ability triggers, returning it from your graveyard to the battlefield with five +1/+1 counters on it.
5. Repeat.

This engine thrives on the clever interplay of Workhorse and Mikaeus, the Unhallowed, transforming a humble mechanical beast into an infinite mana generator. As you strip away the counters from Workhorse to fuel your mana pool, its toughness drops to zero and it hits the graveyard, but Mikaeus grants it undying to bring it right back to the battlefield. To reset this loop permanently, Crovax, Ascendant Hero steps in with a crucial passive ability: its nonwhite-weakening effect instantly shrinks the returning Workhorse back down to zero toughness, bypassing any lingering +1/+1 counters that would otherwise prevent undying from triggering again.