Grenzo, Dungeon Warden + The Cauldron of Eternity + Phyrexian Altar + Dark Ritual + Warden of the Eye

Grenzo, Dungeon Warden

The Cauldron of Eternity

Phyrexian Altar

Dark Ritual

Warden of the Eye

How it works

1. Cast Dark Ritual by paying , adding .
2. Activate Phyrexian Altar by sacrificing Warden of the Eye, adding one mana of any color.
3. When Warden of the Eye dies, The Cauldron of Eternity triggers, putting Warden of the Eye from your graveyard onto the bottom of your library.
4. Activate Grenzo by paying 2, putting Warden of the Eye from the bottom of your library into your graveyard, and then putting it onto the battlefield.
5. When Warden of the Eye enters the battlefield, it triggers, returning Dark Ritual from your graveyard to your hand.
6. Repeat.
7. Once you have infinite mana, you may activate Grenzo's ability any number of times.

This loop transforms Grenzo, Dungeon Warden into an engine for infinite recursion by weaponizing The Cauldron of Eternity's replacement effect, which neatly tucks every dying creature back onto the bottom of your library right where Grenzo's ability can find it. You sacrifice Warden of the Eye to Phyrexian Altar to generate mana and trigger that library-tucking effect, allowing Grenzo's activated ability to instantly cheat the Warden right back onto the battlefield. When Warden of the Eye enters, its triggered ability plucks Dark Ritual out of your graveyard, and casting that ritual provides the exact black mana needed to fuel Grenzo's activation while generating a net surplus along the way.