Slayers/Nightmare Fuel

More prominent in the Light Novel continuity than in the anime...read the first book, then compare it to the anime. There is one scene where Lina and Gourry fight trolls. Swept away by magic in the anime. The novel goes into extreme detail about their bloody reminants, painted all over the inn's walls.
Copy Rezo in the novels...he gains some extra mouths on his body to multiply the number of spells he can use at once. Anime? They're on his hands. Novels? They're his eyes. Physically. That's why they're closed.
Shabranigdo being reborn in the first book...Rezo's flesh melts away, and Shabranigdo himself looks creepy as hell.
Ragnut Rushavna. A spell that turns the victim into a giant hunk of fleshy meat that gets eaten over and over again by snakes. It won't stop until the one who cast the spell is detained, quinessentially making the victim immortal. Never appeared outside the novels for a reason... It's used on a bumbling sorcerer in one of the novels, while the fellow sorcerer who's rivaling him is beheaded. In the anime, they're merely turned to stone.
The novel The Silver Beast follows the story of a cult worshiping Shabranigdo, and most of its members are rather gruesome-looking chimeras. One of them is a skinny beast-like creature with a brain on its back, and both are their own person. A far cry from Zelgadiss...