This can’t be a real enemy anyone can reasonably fight.
Sure it’s real, and it’s also an easy kill. There are a variety of ways to do it. Coriolis fortune with any instant-kill abilities, such as the wizard or rogue have. An assortment of perpetual stuns/disarms from monk, fighter, etc.
I don’t think any particular challenge should require an instant kill ability to be fair. That limits the creative ability to get through the challenge.
While I find it annoying because it hampers my fast farming runs, I respectfully disagree with your other points. You say that it limits the creative ability to get through a challenge, yet in this example you didn’t creatively see a way past it - until I mentioned how it could be done. You just saw a monsters level and HP’s and immediately thought there was some sort of error. It also doesn’t technically require the instant-kill ability, you could solo the thing with nothing but endless Joppa stuns if you wanted.
Personally I think it’s a good idea for the developers to think outside the box, for folks who may care about the “solution” aspect of the game. However for my style I just find it to be a waste of time. When I encounter one of these things I just exit the challenge and start it over at that point, 550 gold is nothing.