Basalt Monolith + Heartstone + Katsumasa, the Animator

Basalt Monolith

Heartstone

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 2, untapping it.
4. Repeat from step 2.

By animating Basalt Monolith into an artifact creature with Katsumasa, the Animator, we cleverly bypass the Monolith's natural aversion to creaturehood while setting up a mana-positive loop. Normally, untapping Basalt Monolith costs three mana, which would just break even with the three colorless mana it taps for—but with Heartstone reducing that untap activation cost by {1}, untapping it now only costs two. This reduction turns the artifact's self-contained untap ability into an infinite engine, yielding an endless surplus of colorless mana.