Voltaic Construct, The Blackstaff of Waterdeep, and Grim Monolith

Prerequisites

• Voltaic Construct on the battlefield
• The Blackstaff of Waterdeep on the battlefield
• Grim Monolith on the battlefield
• Grim Monolith does not have summoning sickness
• available

Steps

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

Results

• Infinite colorless mana
• Infinite untap of artifact creatures you control