Basalt Monolith + Training Grounds + Karn, the Great Creator

Basalt Monolith

Training Grounds

Karn, the Great Creator

How it works

1. Activate Karn's first loyalty ability by putting a loyalty counter on 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 second ability by paying 1, untapping it.
4. Repeat.

To pull off this display of modern alchemy, Karn, the Great Creator plays a crucial role by temporarily turning Basalt Monolith into an artifact creature with his +1 ability, which lets Training Grounds step in to reduce the cost of the Monolith's untap ability. Normally, untapping the Monolith costs three colorless mana, but Training Grounds discounts that activation down to just one mana. Because tapping the Monolith yields three mana while untapping it only costs one, you net two colorless mana each cycle to generate an infinite loop of colorless mana.