Basalt Monolith + Heartstone + Karn, Silver Golem

Basalt Monolith

Heartstone

Karn, Silver Golem

How it works

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

This clever loop transforms a humble artifact into a self-contained engine, fueled entirely by Karn, Silver Golem's ability to animate noncreature artifacts into creatures. While Basalt Monolith would normally cost three mana to untap, Heartstone steps in to reduce that activation cost to two mana, meaning the Monolith taps for three and untaps for two to yield a net positive return of one colorless mana each cycle. Because Karn sets the animated artifact's power and toughness to its mana value rather than stripping away its abilities, Basalt Monolith retains both its tap for three mana and its untap clause, creating an endless loop of infinite colorless mana.