Many people know that Bishibosh (in Cold plains) is immune to fire even on Normal difficulty.
Similarly, Bone Ash (in Cathedral) is immune to cold. So is Coldworm the Burrower in Maggot Lair 3.
But did you know that bosses can be immune to Physical as early as Act 3 Normal?
I just encountered a “Dark Lord” (a type of Vampire) in Durance of Hate lvl 1, and they had the “Stone Skin” modifier which increased their physical resistance from the base of 50% to 100% making them immune to physical damage.
Other super uniques who are immune are
- Witch Doctor Endugu in Flayer Dungeon lvl 3 (fire)
- Grand Vizier of Chaos – the left “seal boss” in Chaos Sanctuary (fire)
- Frozenstein in Frozen River (cold)
- Snapchip Shatter (cold)
- Colenzo the Annihilator (fire)
- Achmel the Cursed (poison)
Honorary mentions:
- Lister the Tormentor 95% resist to poison
- Infector of Souls 90% resist to fire