Mikaeus, the Unhallowed + Phyrexian Altar + Pith Driller

Mikaeus, the Unhallowed

Phyrexian Altar

Pith Driller

How it works

1. Activate Phyrexian Altar by sacrifiicing Pith Driller, adding one mana of any color.
2. When Pith Driller dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
3. When Pith Driller enters the battlefield, it triggers, putting a -1/-1 counter on it.
4. Repeat.

This elegant loop turns a Phyrexian Altar and Mikaeus, the Unhallowed into a self-sustaining engine for infinite colored mana. Mikaeus provides the crucial passive boost: because Pith Driller is a non-Human creature, Mikaeus grants it undying, allowing it to return from the graveyard whenever it perishes. When Pith Driller enters the battlefield with its returning +1/+1 counter, its own triggered ability forces you to place a -1/-1 counter on it, which cleanly annihilates the +1/+1 counter through state-based actions. This leaves Pith Driller completely clear of counters and ready to be sacrificed to the Altar all over again, fueling your mana pool while generating boundless death, entry, and sacrifice triggers.