Basalt Monolith + Agatha of the Vile Cauldron + Xenic Poltergeist

Basalt Monolith

Agatha of the Vile Cauldron

Xenic Poltergeist

How it works

1. Activate Xenic Poltergeist by tapping it, causing Basalt Monolith to become an artifact creature until end of turn.
2. Activate Basalt Monolith's first ability by tapping it, adding CCC.
3. Activate Basalt Monolith's last ability by paying at most 2, untapping it.
4. Repeat from step 2.

This clever loop turns a heavy metal rock into a self-sufficient mana engine, starting with Xenic Poltergeist temporarily animating Basalt Monolith into an artifact creature. Once animated, Agatha of the Vile Cauldron steps in as the mastermind, her passive ability leveraging her power to discount the cost to untap Basalt Monolith down to just two generic mana. Because the Monolith taps to produce three colorless mana and costs only two to untap itself thanks to the discount, you are left with a net gain of one colorless mana with every single iteration.