Right now the only challenging enemy to face is The Nightmare (hard to tell when he's attacking). Is it possible to be able to fight more than just 1 merc ?
Some Red merc are clearly better than other (Demoman can literally kill anyone in one hallway attack) as well but i don't think it should be changed so people can choose their own difficulty . But sometimes i didn't even kill the blue merc at all since they are not aggressive even in MGE mode, i think they should be more aggressive more to give the game more of a challenge.