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

Berta, Wise Extrapolator

Assassin Den

Heartstone

Zirda, the Dawnwaker

How it works

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

This engine transforms Assassin Den's creature-buffing activation into a self-sustaining loop by heavily discounting its cost through the combined static reductions of Heartstone and Zirda, the Dawnwaker. Because those cost-reducers bring the activation fee down to just {U}, every time Assassin Den targets Berta, Wise Extrapolator, Berta's triggered ability responds to the resulting +1/+1 counter by refunding that exact mana. This creates an infinite cycle of counters on your creatures and generates endless mana of any color, all fueled by Berta, Wise Extrapolator's versatile talent for converting growth into resources.