Basalt Monolith, Xenic Poltergeist, and Agatha of the Vile Cauldron

Prerequisites

• Basalt Monolith on the battlefield
• Xenic Poltergeist on the battlefield
• Agatha of the Vile Cauldron on the battlefield
• Basalt Monolith and Xenic Poltergiest do not have summoning sickness

Steps

1. Activate Xenic Poltergeist by tapping it, 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