Arthropleura

Eight feet of armored segments, moving with the low, deliberate certainty. The legs are the worst part - not the count, but the sound. A dry, rhythmic clicking on stone that you feel before you hear it. Territorial, not aggressive by default - it hunts when hungry, ignores the party if it has recently fed. A fed Arthropleura (roll d6 on entry: 1-2 fed, 3-6 hungry) will move away from torchlight unless cornered. A hungry one locks onto the nearest warm body. It does not retreat - no survival instinct for flight, only feeding. A dead Arthropleura yields approximately 40 lbs of chitin segments worth 15 GP to an armorer, and the mandibles worth 8 GP as exotic curiosities. Carrying either is cumbersome and smells of wet cave for days.

Surge: Once per encounter, the Arthropleura rears its front third upright and slams down. All creatures within 5 ft in a forward arc: DEX Quick Save TN 14 or knocked down for 2 rounds and pushed 10 ft back, 1d8+2 bludgeoning. DR applies.

Carapace: Slashing and piercing weapons deal -1 damage per hit due to the segmented chitin. Bludgeoning weapons deal full damage and ignore this reduction. Fire deals full damage and ignores DR.