Ostoyae

A hulking amalgamation of mushroom caps and mycelium, the ostoyae is born of the enokitake and dies in their service. Merged flesh and consciousness make up the towering creature, forming a robust, treelike body with a mushroom canopy. The ostayae grows ever stronger as more enokitake combine with it, recovering from injury and gaining strength with each life that is given. However, a bright candle cannot burn for long—an ostoyae perishes after mere 24 hours of life. The enokitake do not take the creation of this entity lightly, giving their lives in service of the tribe. An ostoyae is a living testament to the power of cooperation and family, rewarding the enokitake’s sacrifice with overwhelming power in service of their defense.


OSTOYAE

Gargantuan plant, lawful neutral

Armor Class 23 (natural armor)
Hit Points 234 (12d20 + 108)
Speed 60 ft.

STR DEX CON INT WIS CHA
28 (+9) 6 (-2) 28 (+9) 16 (+3) 22 (+6) 17 (+3)

Saving Throws Str +14, Con +14, Int +8, Wis +11
Skills Nature +13, Perception +16
Damage Resistances poison, psychic
Condition Immunities stunned, unconscious
Senses blindsight 120 ft., passive Perception 26
Languages sign language
Challenge 16 (15,000 XP); for every additional enokitake that merges with the ostoyae beyond the initial three, increase its CR by 1


TRAITS

Death Throes. When the ostoyae dies, it explodes in a wave of concussive force. Each enemy creature within 300 feet of it must succeed on a DC 22 Constitution saving throw or be knocked unconscious for 1 hour.
Greater Than the Sum of Its Parts. When an enokitake merges with an ostoyae, the ostoyae’s current hit points and hit point maximum increase by 78 (4d20 + 36), and its dimensions increase by 5 feet in every direction. An ostoyae can have a maximum of ten enokitake merged with itself at any given time (including the three that formed it). An ostoyae and any enokitake that merged with it die 24 hours after it is formed.
Guardian of the Enokitake. The ostoyae cannot be compelled or forced to act in a manner that would go against the interests of its tribe.
Legendary Resistance (3/Day). When the ostoyae fails a saving throw, it can choose to succeed instead.
Overpowering Strikes. The ostoyae has advantage on attack rolls against creatures smaller than it, and it deals an additional 19 (3d12) damage when it hits such creatures with its attacks.


ACTIONS

Multiattack. The ostoyae makes three attacks, or one attack and one other action.
Hurl. Ranged Weapon Attack: +14 to hit, range 150/300 ft., one target. Hit: 31 (4d10 + 9) bludgeoning damage. Anything the ostoyae throws with this attack takes 31 (4d10 + 9) bludgeoning damage when it collides with a solid object or surface.
Kabloom (Recharge 5–6). The ostoyae projects a 300-footlong, 5-foot-wide line of green energy from its mouth. Everything in that line must attempt a DC 22 Dexterity saving throw, losing 70 (20d6) hit points on a failure, or half as much on a success. A creature reduced to 0 hit points from this effect is transformed into spores that grow into an enokitake child within 2d6 hours.
Naturalize. The ostoyae touches an object, creature, or magical effect within 15 feet. Any spell of 5th level or lower on the target ends. If the spell is 6th level or higher, the ostoyae makes a Wisdom ability check (+6 bonus) against a DC of 10 + the spell’s level. On a success, the spell ends.
Smash. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 25 (3d10 + 9) bludgeoning damage. Anything within 5 feet of the target is also targeted by this attack.


LEGENDARY ACTIONS

The ostoyae 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 ostoyae regains spent legendary actions at the start of its turn.
Seize. The ostoyae attempts to grapple a creature within reach or picks up an object within reach.
Stride. The ostoyae moves up to 30 feet.
Strike. The ostoyae makes a single attack.
Wind Up (Costs 2 Actions). The ostoyae takes the Ready action to ready an attack against the first target that moves within its reach. On a successful hit, the readied attack deals an additional 35 (10d6) damage.


Ref: TPKB1 p105