Basalt Monolith, Karn, Silver Golem, and Biomancer's Familiar

Prerequisites

• Basalt Monolith on the battlefield
• Karn, Silver Golem on the battlefield
• Biomancer's Familiar on the battlefield
• Basalt Monolith does not have summoning sickness

Steps

1. Activate Basalt Monolith's first ability by tapping it, adding
2. Activate Karn by paying , making Basalt Monolith a 3/3 artifact creature until end of turn
3. Activate Basalt Monolith's last 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