Berta, Wise Extrapolator, Assassin Den, Heartstone, and Zirda, the Dawnwaker

Prerequisites

• Berta, Wise Extrapolator on the battlefield
• Assassin Den on the battlefield
• Heartstone on the battlefield
• Zirda, the Dawnwaker on the battlefield
• available

Steps

1. Activate Assassin Den by paying due to Zirda and Heartstone, putting a +1/+1 counter on Berta
2. Berta triggers, adding
3. Repeat

Results

• Infinite +1/+1 counters on a creature