Magic: The gathering - Vebulid

Another Phyrexian horror illustrated by Ron Spencer, this big, slimy sac of guts had a unique card mechanic; its power and toughness (attack and hp, basically) grow every single turn automatically, but the Vebulid dies if it ever attacks, so it's sort of like a kamikaze balloon monster. When I first saw the artwork, I thought it was a floating creature with two insect-like arms, but if you look at the background, it has a third appendage. It's an organic tripod!

Magic: The Gathering - Souldrinker

This guy's not another "horror" card, but a "spirit," interestingly enough. The pale, blind, saclike monster with very human arms makes a really eerie visual, and if you want a better idea of its anatomy, there's another one floating like a jellyfish far in the background (lower right!)