Basalt Monolith, Katsumasa, the Animator, and Agatha of the Vile Cauldron

Prerequisites

• Basalt Monolith on the battlefield
• Katsumasa, the Animator on the battlefield
• Agatha of the Vile Cauldron on the battlefield
• undefined 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 at most , untapping it
4. Repeat from step 2

Results

• Infinite colorless mana