Gargantuan undead, neutral

Armor Class: 14 (natural armor)

Hit Points: 234 (14d20 + 80)

Speed: 0 ft

STR

10 +0

DEX

8 -1

CON

21 +5

INT

24 +7

WIS

16 +3

CHA

16 +3

Saving Throws: STR (+12), CON (+10), INT (+9)

Skills: Insight (+8), Perception (+10)

Damage Vulnerabilities: Fire

Damage Resistances: Necrotic, Nonmagical Bludgeoning, Piercing, & Slashing

Damage Immunities: Poison

Condition Immunities: Charmed, Frightened, Grappled, Incapacitated, Paralyzed, Petrified, Poisoned, Prone, Restrained, Stunned

Senses:

• Blindsight. 120ft.
• Passive Perception: 16

Languages: understands all of the languages that its victims knew in life but can't speak

Challenge Rating: 15

Actions

• Shriek (Recharge 5-6). Each creature of the Proto-Gravemind's choice that is within 120ft. of the Proto-Gravemind and aware of it must succeed on a DC 18 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Legendary Actions

The Proto-Gravemind can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Proto-Gravemind regains spent legendary actions at the start of its turn.

• Biomass Shell. The Proto-Gravemind channels nearby biomass to form a protective shell, granting itself 15 (2d6 + 8) temporary hitpoints.
• Focus Flood. The Proto-Gravemind selects one creature. The next attack against the chosen creature is made with advantage.
• Mucus. The Proto-Gravemind causes a layer of mucus to form over all surfaces within 60ft. of it that lasts for 1 round. Surfaces coated in the mucus are treated as difficult terrain.

Lair Actions

On initiative count 20 (losing initiative ties), the Proto-Gravemind takes a lair action to cause one of the following effects; the Proto-Gravemind can't use the same effect two rounds in a row.

• Summon Flood Crawlers. 4 Swarms of Flood Crawlers form from biomass in an unoccupied space within 60ft. of the Proto-Gravemind.
• Summon Flood Screechers. 2 Swarms of Flood Screechers form from biomass in an unoccupied space within 60ft. of the Proto-Gravemind.
• Summon Flood Stalkers. 4 Flood Stalkers form from biomass in an unoccupied space within 60ft. of the Proto-Gravemind.
• Summon Flood Combatants. 4 Flood Combatants form from biomass in an unoccupied space within 60ft. of the Proto-Gravemind.
• Summon Flood Carriers. 4 Flood Carriers form from biomass in an unoccupied space within 60ft. of the Proto-Gravemind.
• Summon Flood Dragon Wyrmling. 1 Flood Dragon Wyrmling forms from biomass in an unoccupied space within 60ft. of the Proto-Gravemind.