If you really want to play a three-drop Merfolk badly, theres Hullbreacher (well, not in Commander, but it was too good!)
X s Giga Burn for 120, and Drapions Derail for 60+ (with Special D Energy) with the added effect of discarding all special energy attached to the defending Pokmon
Witherbloom is big, flashy, and surprisingly efficient once the engine gets moving
And of course, our ramp package has to include CultivateCultivate and Kodama's ReachKodama's Reach
He played it as a generic mono-blue build, with control, big creatures, and various stuff including mill
There seem to be no limits on the amount of energy you can claim, so some players have been facing some problems when going into battle against a Misty user