Entropy Worm

Gargantuan aberration, unaligned

An Entropy Worm is a planar organism: a living creature that exists primarily in the Void and travels through the boundary between planes the way an earthworm travels through soil. Only a cross-section of the Worm is visible in the material plane at any given time; the full organism extends for miles in both directions, existing mostly in the Void.

Armor Class:18 (natural armour)

Hit Points:300 (at the vulnerable joint between segments)

Speed:10 ft. (constant passage, cannot be altered)

Challenge:CR 15

STR

28 (+9)

DEX

6 (-2)

CON

26 (+8)

INT

3 (-4)

WIS

16 (+3)

CHA

1 (-5)

Saving Throws:CON +14, WIS +9

Damage Resistances:All other damage types

Damage Immunities:Cold, necrotic, poison, psychic

Condition Immunities:All conditions

Senses:Tremorsense 300 ft., passive Perception 13

Traits

Regeneration. The Worm regains 20 HP at the start of each turn. Suppressed for 1 round by 30+ radiant damage in a single turn. Suppressed for 2 rounds if dealt at the vulnerable joint.

Planar Anchor. The Worm's presence maintains any Breach it is passing through. The Breach cannot be sealed while the Worm is alive and present.

Geological Awareness. Tremorsense 300 ft. Does not distinguish between creatures. Reacts to damage, not presence.

Indifferent Mass. Cannot be pushed, pulled, grappled, restrained, or moved by any effect.

Segment Shift (Recharge 5-6). The Worm adjusts position. All creatures within 30 feet: DC 19 STR save or 6d10 bludgeoning + 20 ft push. Save: half damage, 10 ft push.

Void Wake. At the start of each round, all creatures within 60 feet: DC 16 CON save or 4d8 cold damage.

Spawn Soldiers. When the Worm first takes 50+ damage in a single round, it ejects 4 Void Soldiers from its tissue. These soldiers are fully formed and act on initiative count 10.

Legendary Actions

3 per round, at end of other creatures' turns:

Tremor. All creatures within 30 feet: DC 16 DEX save or fall prone.

Void Exhalation (2 actions). 30-foot cone, DC 18 CON, 5d8 cold + 1 exhaustion. Save: half, no exhaustion.

Segment Shift (3 actions). As above.