Barrenton Medic, Agatha's Soul Cauldron, and Incubation Druid

Prerequisites

• Barrenton Medic in exile
• Agatha's Soul Cauldron on the battlefield
• Incubation Druid on the battlefield
• minus for each +1/+1 counter on Incubation Druid available

Steps

1. If Incubation Druid does not have a +1/+1 counter on it, activate its adapt ability by paying , putting three +1/+1 counters on it
2. Activate Incubation Druid by tapping it, adding
3. Activate Incubation Druid using Barrenton Medic's second ability by putting a -1/-1 counter on it, untapping Incubation Druid
4. Repeat

Results

• Infinite colored mana