*Glitch Still Works As of Aug 6 2020*
I was able to use the glitch in this video to beat Hell on Earth difficulty with a level 5 Berserker
using the starting shovel and the Skirmisher
perk to have health regen, also the boss I went up against was the Abomination
and if he moves into the corner you can sometimes force him outside the map which kills him instantly but if that doesn't happen it's easy enough to melee him to death.
Basics of the glitch spot are that you crouch inside a pile of boxes on the Desolation map that enemies are unable to see you or damage you if you are positioned correctly and you can melee them infinitely. This spot could potentially be used by any class but Berserker
is definitely one of the easier ones as they start with a melee weapon and are unable to be grabbed.