Awesome pictures. All 3 of those look great
As far as the uncommon hero bit, it isn't a big deal for me because it doesn't do anything for the design mechanically, but in later comics (pictured below) and the Wolverine and X-Men cartoon they had organizations like SHIELD developing multiple Wendigos as super soldiers. I figured since the guys that have turned into Wendigo are each pretty forgettable characters, an uncommon hero wouldn't be so bad and it could actually be fun to go up against like 3 of them in an army match.
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I had intended for Wendigo to be able to go up against Hulk and at least stand a chance. I figured this would put him somewhere in the 340-380 range. If we dropped his attack to 7 it would probably mean upping his stats in other areas (maybe life?) but I feel like the design in theory is pretty balanced right now.
For the frenzy power I was intending for him to be able to chain multiple Unique Hero kills and subsequent additional turns as this could be tough to pull off, but would be a lot of fun to try and set up. Strategically you'd go in first with a multi-attacker and soften up some of the heroes and try to bring in Wendigo to finish off the weak. Also weak supporting heroes like Alfred, Riddler, Destiny, etc would have a huge target on their forehead for a hungry hungry Wendigo.
Again I haven't tested out the design yet, but would be okay with dropping the attack or limiting the additional turn to 1 per OM if it meant getting a balanced and fun design within the 340-380 range.