Basalt Monolith, Katsumasa, the Animator, and Heartstone

Prerequisites

• Basalt Monolith on the battlefield
• Katsumasa, the Animator on the battlefield
• Heartstone on the battlefield
• Basalt Monolith does not have summoning sickness
• available

Steps

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

Results

• Infinite colorless mana