They Came from the Moon! A Space-Breaking Monster

Within his cyclopean moon-fortress, in his court of archons, the Machine Sage plots and schemes. In his Byzantine cauldrons he spawns his dread minions. Among them, the menacing sentinel, the looming lunar terror, the savage...

MOON-CRAB!

Not what I expected when I looked up 'Moon Crab,' but I'll go along

This year's Secret Santicorn (my first!) is already a big success, with some forty people participating! Here's my post for out friendly neighborhood Machine Sage. Happy Goblindays!

Prompt: A monster or two based around breaking space. Escher Dragons, 2D Orcs, etc.

Moon-Crab
HD 3 (10 HP) DEF 8 ATK 14(spearing claw) MOR 10 MOV 2x sideways
Treasure: An intact Moon-Crab can be dried and used as fine vellum(50gp). Otherwise, its shell can be peeled off and treated to become flexible, can make 10' of Moon-Rope, resistant to heat, cold and the vacuum of space, easily cut but never torn or frayed (10gp).
2-Dimensional: See below
# Appearing: 1(sentinel) 1d4+2(excursion) 2d4+3(landing)

When dormant, lies on the ground, can sense sound through contact with the ground. Visible, appears as a disgusting carpet of roiling innards. When alerted, jumps up to become vertical. It rotates on its own axis. A pulsing mass of organs, blood vessels and chitin, widening to reveal the outline of a giant crustacean-like creature, armed with a long, piercing claw. It rotates to see the world around it in an approximation of three dimensions.

When fully perpendicular to a character, its outline is the horizontal cross-section of a crab, standing up on its backmost legs, innards exposed.

At the start of each round, it selects a character. This is the character it can 'see' and will engage in combat with them. It becomes 'invisible' to that character by turning their body parallel to their point of view, appearing only as a vague vertical shimmer in the air. It can only move backwards and forwards like this, either charging or fleeing.

The character being targeted suffers a -8 to hit, both because of the creature's armor now facing them and because it is effectively invisible. All other characters can see at least some part of it. These characters are able to see its insides and disregard its external armor, effectively cutting holes in a paper target.

This monster serves to encourage teamwork in the party. A lone character will have little chance of defeating it, but even a single other character will be able to take advantage of its blindness. Adding more into the fight dramatically scales up the challenge, and unless the players can coordinate to focus on one at a time, they will surely be overwhelmed.

Right feel but, you know, not a crab