Activate the Forest or Island by tapping it, adding {G} or {U}.
Cast Earthen Arms for its awaken cost by paying {6}{G}, putting two +1/+1 counters on Gilder Bairn, and causing the Forest or Island to become a 0/0 Elemental creature that is still a land, and putting four +1/+1 counters on it.
Activate Experiment Kraj using the Forest or Island's ability by tapping it, adding {G/U}.
Activate Experiment Kraj using Gilder Bairn's ability by paying {G/U} and untapping it, doubling the counters on target permanent.
Repeat from step 3.

Infinite proliferate

Combos with "Earthen Arms"