For Prince in HM UK what I like to do with my 4DK + healer team is to use my 4x army of the dead as it makes him a complete joke...and there is no need to save them for 2nd boss or Ingvar anyway. Prince will just shoot 1 zombie at a time ignoring your team (if you have AMZs, drop them here as well) ...its sad really, you dont even need to heal...I think I might use a rejuv or 2 over the entire battle. I've always killed frost tombs but i'm sure the fight is perfectly doable ignoring them if you wanted the achievement. Outside of the frost tombs though I just focus fire prince and ignore skeletons as they get automatically picked up from my tanks UB or a random zombie