Gilder Bairn + Druids' Repository + A Realm Reborn

Gilder Bairn

Druids' Repository

A Realm Reborn

How it works

1. Activate A Realm Reborn 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.