Gilder Bairn + Druids' Repository + Elven Chorus

Gilder Bairn

Druids' Repository

Elven Chorus

How it works

1. Activate Elven Chorus by tapping Gilder Bairn, adding one mana.
2. Activate Gilder Bairn by paying 2G/U and untapping it, doubling each counter on Druids' Repository.
3. Activate Druids' Repository as many times as necessary by removing counters from it, adding at least two mana.
4. Repeat from step 2.
5. Once you have infinite counters on Druids' Repository, you may instead double the counters on any other permanents.