Basalt Monolith, The Blackstaff of Waterdeep, and Zirda, the Dawnwaker

Prerequisites

• Basalt Monolith on the battlefield
• The Blackstaff of Waterdeep on the battlefield
• Zirda, the Dawnwaker on the battlefield
• available

Steps

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

Results

• Infinite colorless mana