Mikaeus, the Unhallowed + Workhorse + Heartless Summoning

Mikaeus, the Unhallowed

Workhorse

Heartless Summoning

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 clever loop transforms a mechanical beast of burden into an infinite engine for colorless mana and death triggers, fueled entirely by the synergy of Mikaeus, the Unhallowed, Workhorse, and Heartless Summoning. Heartless Summoning provides a crucial discount while its static -1/-1 penalty ensures that Workhorse dies instantly the moment it runs out of counters, bypassing any need for an external sacrifice outlet. Once Workhorse strips itself of its initial charge through its own activation, Mikaeus, the Unhallowed grants it undying so that it returns to the battlefield with a fresh batch of counters, ready to be tapped for mana all over again.