Experiment Kraj + Channeler Initiate + Devoted Druid

Experiment Kraj

Channeler Initiate

Devoted Druid

How it works

1. Activate Experiment Kraj using Devoted Druid's second ability by putting a -1/-1 counter on Experiment Kraj, untapping Experiment Kraj.
2. Activate Experiment Kraj using Channeler Initiate's ability by tapping Experiment Kraj and removing a -1/-1 counter from it, adding one mana of any color.
3. Repeat.