- Goddamned Bats: The gargoyles.
- Heretic II introduces the harpies which are even worse, since they like to hang back very high in the sky, dodge just about everything you can throw at them. Unless you use the homing meteor swarm on them.
- Goddamned Boss: D'sparil's second phase, and not just because his lightning blasts deal a crapton of damage on direct hit, either. He can also summon additional disciples, but on top of that, he starts teleporting more often the lower his health gets.
- I Am Not Shazam: Some of the old FAQs name the protagonist Heretic, since he didn't have a proper name at that time. Funnily enough, just adding "the" in front of it would have made it appropriate...
- Most Annoying Sound: The gargoyles' laughter. Get ready to hear it constantly.
- That One Attack: All the Iron Lich's attacks hit like a freight train, but are fairly easy to dodge...except for the tornado, which chases down the player, lifts them up and flings them around (and can easy hurl the player into a damaging floor if there are any around,) can easily last a very, very long time, and in certain scenarios can absolutely ravage the player's health. The only saving grace is that they get fairly easily hung up on the architecture.
- That One Level: Catafalque (E4M1) follows in the tradition of the first level of Thy Flesh Consumed from Ultimate Doom by being a Drought Level of Doom that also tosses in a boss-level enemy (in this case a Maulotaur) into fray and forces you to fight in tight spaces. Except that Heretic's level is even more stingy with it's pickups, and also throws in four Iron Liches as an extra "Fuck you." Better learn how to kill things with the staff and gauntlets.