Basalt Monolith + Biomancer's Familiar + Katsumasa, the Animator

Basalt Monolith

Biomancer's Familiar

Katsumasa, the Animator

How it works

1. Activate Katsumasa by paying 2, 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 1, untapping it.
4. Repeat from step 2.

To pull off this infinite mana loop, Katsumasa, the Animator does the crucial setup work by turning Basalt Monolith into an artifact creature. This transformation allows Biomancer's Familiar to step in and apply its cost-reduction static ability, slashing the untap cost of Basalt Monolith from three generic mana down to just a single mana. Because tapping Basalt Monolith yields three colorless mana while its discounted untap costs only one, you net two colorless mana with every iteration of tapping and untapping.