Berta, Wise Extrapolator + Assassin Den + Heartstone + Biomancer's Familiar

Berta, Wise Extrapolator

Assassin Den

Heartstone

Biomancer's Familiar

How it works

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

This clever engine turns Assassin Den’s unblockable-granting ability into a self-sustaining loop by heavily discounting its activation cost with both Heartstone and Biomancer's Familiar down to just a single blue mana. When you target Berta, Wise Extrapolator with this discounted activation, the resulting +1/+1 counter triggers Berta's ability to refund your mana, paying for the next iteration entirely. This lets you grow your target creature infinitely large while laundering your mana through Berta's triggered ability.