Activate Experiment Kraj by tapping it, putting two +1/+1 counters onto Devoted Druid.
Activate Experiment Kraj using Devoted Druid's last ability by putting a -1/-1 counter on itself, untapping it.
Activate Experiment Kraj's own ability, putting two +1/+1 counters on itself.
Remove the -1/-1 counter and one of the +1/+1 counters from Experiment Kraj as a state-based action.
Repeat steps 2 through 4 any number of times, resulting in any number of +1/+1 counters on Experiment Kraj.
Activate Experiment Kraj using Devoted Druid's last ability by putting a -1/-1 counter on itself, untapping it.
Activate Experiment Kraj using Devoted Druid's first ability by tapping it, add ({G} magic symbol) .
Repeat steps 6 and 7 any number of times.
You may also activate Experiment Kraj's own ability any number of times instead of step 7, putting any number of +1/+1 counters onto creatures.
Once there are infinite +1/+1 counters on your creatures, you may activate Experiment Kraj using Kami of Whispered Hope's ability any number of times, adding infinite mana of all colors.