That is rough, the Mars Core one is probably the straight out most unfair if only because Prowlers suck.
I don't know why people have such a hard time with these guys, the only two I had any real "trouble" with (I don't count the auto save that put me at 50 health as trouble because "Do it perfect or insta die" is almost everything not an Imp on Nightmere) were The Slayer gate one who had god damn Prowlers with it, and the one right after the Sword that spawns right in the middle of the middle of a fight.
PS : The worst enemy in the game isn't Archviles, Pain Elementals, Doom Slayers or Mauraders..the worst thing in the entire game are the FUCKING GOD DAMN PROWLERS. Why the fuck do imps with teleport require 3 chainsaw gas to kill?