#cr27

Attributes

Tiny ooze, chaotic neutral

Armor Class: 19 (natural armor)

Hit Points: 250 (20d4 + 200)

Speed: 20 ft., climb 20 ft.

STR: 2 (-4)

DEX: 10 (+0)

CON: 30 (+10)

INT: 2 (-4)

WIS: 3 (-4)

CHA: 2 (-4)

Saving Throws: CON +18

Skills: Perception +4

Damage Vulnerabilities: fire

Damage Immunities: necrotic, poison; bludgeoning, piercing, and slashing damage from nonmagical attacks

Condition Immunities: blinded, charmed, deafened, frightened, grappled, paralyzed, petrified, poisoned, prone, restrained, stunned, unconscious

Senses: blindsight 60 ft. (blind beyond this distance), passive Perception 14

Languages: none

Challenge: 27 (105,000 XP)

Proficiency Bonus: +8

Special Traits

Convert. Any time a creature or object makes physical contact with gray goo, the goo attaches itself and attempts to make more gray goo. This effect even occurs if the gray goo has been killed; destroying the goo's body is the only way to end this effect.

Objects that a gray goo touches are cursed to turn into more gray goo over time. This time period differs by the target: 1 hour for a square foot of terrain or liquid; 1 hour per pound of a mundane object; or 1 month for magic items. Small or Tiny objects become 1 gray goo, and larger objects become 1 gray goo per 10 pounds of the object's weight. Spells or effects that remove curses prevent the gray goo conversion if the curse is removed before the transformation is complete.

Every time a creature makes physical contact with gray goo, it must succeed on a DC 22 Constitution saving throw or become cursed. While cursed in this manner, any time the creature takes damage, the creature's hit point maximum is reduced by the amount of damage taken, and this hit point maximum reduction cannot be removed. If the creature's hit point maximum is reduced to 0, the creature dies and its body becomes more gray goo (1 gray goo per 50 pounds of the creature's body weight, minimum 1). If the curse is removed, the creature's hit point maximum is restored after a long rest.

Pack Tactics. The gray goo has advantage on attack rolls if an ally is within 5 feet of the target and isn't incapacitated, or if the target is a creature cursed by a gray goo's Convert feature.

Actions

Pseudopod. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 7 (2d6) bludgeoning damage, or 14 (4d6) bludgeoning damage if its target is a creature cursed by a gray goo's Convert feature.

[id: monster stat block for gray goo, depicting an elf with their hand converting to gray goo, turning amorphous and partly transparent]