Night Twist, Ancient (CR 20)

Huge Plant
Alignment: Always neutral evil
Initiative: -2 (Dex); Senses: low-light vision, Listen +17, and Spot +18
Languages: Common, Elven, and Sylvan

AC: 38 (-2 size, -2 Dex, +26 natural, +6 deflection), touch 12, flat-footed 38
Hit Dice: 25d8+300 (412 hp); DR: 15/slashing
Fort +32, Ref +12, Will +19
Speed: 10 ft.
Space: 15 ft./25 ft.
Base Attack +18; Grapple +43
Attack: Slam +33 melee (4d6+17) or
6 slams +33 melee (4d6+17)
Special Attacks/Actions: Death curse, despair song, spell-like abilities, wind blast
Abilities: Str 45, Dex 6, Con 34, Int 12, Wis 16, Cha 23
Special Qualities: plant traits, unholy grace, vulnerability to fire
Feats: Blind-fight; Diehard; Endurance; Improved Natural Armor (3); Improved Sunder; Iron Will; Power Attack
Skills: Hide +60, Knowledge (nature) +18, Listen +17, Move Silently +8, and Spot +18
Advancement: 26-48 HD (Huge)
Climate/Terrain: Temperate marshes
Organization: Solitary
Treasure/Possessions: Standard coins, no goods, standard items

Source: Monster Manual III

In addition to the special abilities and qualities inherent in a younger specimen (Night Twist), an ancient night twist has even deadlier powers and spell-like abilities in its arsenal. This creature uses its spell-like abilities before resorting to its powerful slam attack. The save DCs (DC 28) for an ancient night twist's death curse, despair song, and wind blast are adjusted for its higher Charisma score and increased Hit Dice.

Spell-Like Abilities: 5/day - phantasmal killer (DC 20); 3/day - blight (DC 21), circle of death (DC 22), deeper darkness, entangle (DC 17), fear (DC 20), insanity (DC 23); 1/day - weird (DC 25). Caster level 20th.