As tall as a human, this over-sized, disembodied rib cage floats through the air. Having no sternum, it snaps its jagged ribs like teeth on a pair of jaws.
Bone Cage (CR 5)
NE Medium undead Init +2; Senses blind, blindsight 60 ft.; Perception +7
--- AC 18, touch 12, flat-footed 16 (+2 Dex, +6 natural) hp 52 (7d8+21) Fort +4, Ref +4, Will +6 DR 5/bludgeoning; Immune blind, undead traits
--- Speed fly 30 ft. (perfect) Melee bite +11 (1d8+7 plus grab) Special Attacks en-cage, ram
--- Str 21, Dex 15, Con —, Int 2, Wis 13, Cha 14 Base Atk +5; CMB +10 (+12 bull rush, +14 grapple); CMD 23 (25 vs. bull rush) Feats Improved Bull Rush, Power Attack, Toughness, Weapon Focus (bite) Skills Fly +10, Perception +9 Languages Common (can't speak)
--- Environment any land or underground Organization solitary or block (2–5) Treasure none
--- En-Cage (Ex) Whenever a bone cage pins a creature of its size or smaller with a grapple maneuver, it traps that creature within its rib cage. The bone cage may still not use its bite attack while maintaining the pin, but does not have the grappled condition. Ram (Ex) When maintaining a pin using its en-cage ability and also performing a bull rush maneuver, a bone cage batters the bull rushed creature with the pinned creature. If the bull rush attempt succeeds, the bull rushed creature and the pinned creature each take 1d6+7 points of bludgeoning damage. This damage includes the bone cage's Strength modifier time one-and-a-half.
Formed from the harvested rib cage of a larger-than-human creature, a bone cage is a flying undead monstrosity that can entrap victims inside its skeletal body. No sternum holds the bone cage's ribs together, allowing it to use its ribs like teeth, biting, grabbing, and pinning victims. When a bone cage's mouth is occupied with a pinned victim, it can use its unfortunate victim as a battering ram.
The exact method of creating a bone cage is unknown to the general population, and is a matter of much speculation. Some see a special purpose in the peculiar anatomy of the bone cage, speculating that the creature was originally developed as an undead prison guard, able to restrain targets without killing them when instructed to do so by its masters. Others suspect that the bone cage is instead the product of opportunistic necromancy, using leftover parts in the most efficient manner possible given the limitations of their shape.