Cave Demon Crab (3.5e Monster)

It's some kind of harmless cave cra- OH GOD MY EYE MY EYEEEE!!!!!

Rumored to be some sick joke played by a god after someone made a killer bunny rabbit, the cave demon crab is, in all respects, a normal cave crab but for one exception; it is an unstoppable force of doom which destroys all it touches. No one believes it at first, but nothing short of massive damage and epic weapons will stop its threat. Fortunately most cave demon crabs are neutral and will happily go about their business living boring, crabby lives. It is not until provoked does the threat come to bear. If its victim does not run for their life they will become marked, hunted down until the end of their days with no hope for relief except in death.

Cave demon crabs do not speak, but usually understand common. They seem to have no desires beyond that of a typical crab.

Combat
You do not engage the cave demon crab, you run, you run far away! If somehow you manage to survive a few rounds with it without dying or retreating, it will mark you to met out its revenge on its own time.

Attach : If a cave demon crab hits with a claw attack, it uses its powerful grip to latch onto the opponent’s body and automatically deals claw damage each round it remains attached. An attached cave demon crab loses its Dexterity bonus to Armor Class and has an AC of 34. An attached cave demon crab can be struck with a weapon or grappled itself, though there is a 50% chance you will hit the victim instead. To remove an attached cave demon crab through grappling, the opponent must achieve a pin against the creature.

Carapace : The cave demon crab's armorlike carapace is exceptionally tough and highly reflective, deflecting all rays, lines, cones, and even magic missile spells. There is a 30% chance of reflecting any such effect back at the caster; otherwise, it is merely negated. Check for reflection before determing if its Magic Immunity ability absorbs it.

Damage Reduction : The cave demon crab's damage reduction is so tough it can ignore the effects of maneuvers and other effects which ignore damage reduction and hardness, such as foehammer.

Frightful Presence : The cave demon crab can inspire terror by simply willing it as a free action. Affected creatures must succeed on a DC 30 Will save or become shaken, remaining in that condition as long as they remain with 60 feet of the cave demon crab. The save DC is Charisma-based.

Immunities : Cave demon crabs are immune to acid, cold, electricity, fire, force, and sonic damage. They are immune to ability damage, ability drain, energy drain, exhaustion, fatigue, mind-affecting effects, nausea, paralysis, petrification, poison, polymorphing, sickening, and stunning. Finally it is immune to critical hits and sneak attacks.

Magic Immunity : As if their powerful damage reduction or reflective carapace weren't enough, cave demon crabs are completely immune to any spell which offers spell resistance.

Mark of Doom :  As a free action as part of an attack, a cave demon crab can curse a creature to become its prey. From this point on, a cave demon crab can duplicate the effects of shadow walk at will, if only to travel between its lair and its cursed target. Those who have been cursed are followed with the greatest of vengence, patiently stalked and attacked when they least expect it. They try to sleep, CRAB BATTLE! They are in the middle of battle with someone else, CRAB BATTLE! They open the cupboard to get some breakfast, BLAMMO! CRABS HAVE YOU FOR BREAKFAST!

Fortunately cave demon crabs can only have one such mark of doom at a time. If they apply another, the first is removed. Marks of doom are a curse and can only be released with limited wish, miracle, or wish, or a remove curse of caster level 31st or higher. The saving throw against mark of doom is a Will DC 45, save negates. The saving throw is Charisma based.

Murderous Presence : The reason cave demon crabs are so difficult is that their ego is so overwhelming it bends reality to their will. Cave demon crabs recieve their Charisma modifier to attack, damage, ability checks such as grapple and initiative, as a deflection bonus to AC, to all saving throws, and as a bonus to all saving throws. They also count their Charisma to their effective HD for the purposes of spells and effects.

Rush : Once per minute, the normally slow-moving cave demon crab can move at a speed of 200 feet.

Severing Claws : On a natural 20 attack roll a cave demon crab can remove a limb or body part with the appropriate penalties for the loss, including the head which typically kills a creature. This deals an additional 1d6 Con damage and requires regeneration or higher magic to restore the missing body part. Many crabs choose to merely mangle rather than kill, apparently self aware that the survivors will keep others far away from their territory.

The claws are unnaturally sharp and cut through any damage reduction, as well as counting as lethal damage against regeneration. They are ghost touched, and may strike incorporeal creatures as well as material ones.