I'm surprised Chrome Dome and Muckman haven't appeared in IDW to this day
 

IDW TMNT debuted the vast majority of old Fred Wolf/Playmates/Archie mutant characters. But Chrome Dome and Muckman never appeared in IDW. Chrome Dome is just a robot, he would be the easiest to work in. And Muckman could just be another mutant town mutant, some guy who got mutated with sludge or backteria when Hob's mutant bomb went off.

I'm surprised they have yet to appear. Also why did IDW kill off Wingnut/Screwloose in like 1 issue during the Bebop/Rocksteady world tour from a couple years ago? Weird way to use them.

Why? He's literally a walking pile of compost, it's too gross and weird to take seriously.

Because I want to see try-hard body horror IDW Muckman and Joe Eyeball, and that’s good enough for me.

The Last Ronin is such a piece of garbage that I consider it the IDW version of Muckman.

Correct me if I’m wrong, but Lord Dregg hasn’t been adapted by IDW yet either, has he?

At this point it is more impressive when they don't adapt an pre-existing cartoon character than when they do.

I mean a lot of the more recent IDW original characters have been pretty meh or forgettable characters. I can't remember who the last well received original character was, probably dating back to the first 50 issues with Old Hob, Alopex, Koya, Bludgeon, etc. Did we get any memorable original characters since?

Nah, but we haven't even seen Maligna return yet either from years ago

Vernon Fenwick appeared in The Armageddon Game arc, but he is later killed. They brought some villains from other series to IDW TMNT, but most of the time, the main rivals have always been Foot Clan and Krang.