Updated the main post with some spoilage info.
Given his manifestation requirements and the general abilities he seems to grant, my guess is that his Avatar version will mostly change Som'er's style of play by forcing him to stick with his crew more than his Master form. I've found as a Master he can tend to play rather statically, being a summoning "portal" in the back of the board while throwing his horde of minions forward.
Personally, I love that change of pace a LOT. Gremlins are a very synergistic group for the most part. You've got Som'er, Hog Whisperer, Slop Haulers, Taxidermist, and now Lenny providing utility/synergy/buffing to your "basic" Bayou Gremlin and Pig minions. It seem snow Som'er has a greater incentive to move around with the group than he did previously, because once you Manifest you're going to want him near the front lines to provide his buffs and be a beatstick, rather than sitting back and summoning constantly.