Basalt Monolith, Karn, the Great Creator, and Agatha of the Vile Cauldron

Prerequisites

• Basalt Monolith on the battlefield
• Karn, the Great Creator on the battlefield
• Agatha of the Vile Cauldron on the battlefield
• Basalt Monolith does not have summoning sickness
• Agatha of the Vile Cauldron has power 1 or greater

Steps

1. Activate Karn's first loyalty ability by putting a loyalty counter on it, causing Basalt Monolith to become a 3/3 artifact creature until end of turn
2. Activate Basalt Monolith's first ability by tapping it, adding
3. activate Basalt Monolith's second ability by paying at most , untapping it
4. Repeat from step 2

Results

• Infinite colorless mana