Gilder Bairn + Pentad Prism + Earthcraft

Gilder Bairn

Pentad Prism

Earthcraft

How it works

1. Activate a basic Forest or Island by tapping it, adding G/U.
2. Activate Earthcraft by tapping Gilder Bairn, untapping the basic Forest or Island.
3. Activate the Forest or Island by tapping it, adding G/U.
4. Activate Gilder Bairn by paying 2G/U and untapping it, doubling each counter on Pentad Prism.
5. Activate Pentad Prism as many times as necessary by removing counters from it, adding at least two mana.
6. Repeat from step 2.
7. Once you have infinite counters on Pentad Prism, you may instead double the counters on any other permanents.