Gilder Bairn + Druids' Repository + Splinter Twin

Gilder Bairn

Druids' Repository

Splinter Twin

How it works

1. Activate Splinter Twin by tapping Gilder Bairn, producing its effect.
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 three 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.