Basalt Monolith + Biomancer's Familiar + Karn, Silver Golem

Basalt Monolith

Biomancer's Familiar

Karn, Silver Golem

How it works

1. Activate Basalt Monolith's first ability by tapping it, adding CCC.
2. Activate Karn by paying 1, making Basalt Monolith a 3/3 artifact creature until end of turn.
3. Activate Basalt Monolith's last ability by paying 1, untapping it.
4. Activate Basalt Monolith's first ability by tapping it, adding CCC.
5. Repeat from step 3.

This ingenious loop hinges on turning Basalt Monolith into an animate creature using Karn, Silver Golem, which drops its untap ability's activation cost down from three mana to a single mana thanks to Biomancer's Familiar reducing the cost of creature abilities. Because tapping the Monolith yields three colorless mana while the newly discounted untap ability costs only one, you net two colorless mana with every iteration. The Familiar and Karn transform a normally self-contained mana rock into an engine that generates infinite colorless mana.