Crystalline Monolith

Lair Actions

On initiative count 20 (losing initiative ties), the crystalline monolith takes a lair action to cause one of the following magical effects; the crystalline monolith can’t use the same effect two rounds in a row:

  • The crystalline monolith creates an illusory duplicate of itself in its space. The double moves or speaks according to the monolith’s mental direction. Each time a creature targets the monolith with an attack, roll a d20 to determine whether the attack instead targets the duplicate. On a roll of 11 or higher, the attack hits and destroys the duplicate. A creature can use its action to make a DC 15 Intelligence (Investigation) check to determine which monolith is real. On a success, the creature identifies the illusion. The duplicate is intangible, but otherwise is identical to the monolith by sight, smell, or hearing. The duplicate lasts for 1 minute or until the monolith uses this lair action again.
  • The crystalline monolith vibrates at a frequency that reverberates through the lair, causing the ground to tremble. Each creature on the ground, other than the monolith, within 60 feet of it must succeed on a DC 15 Dexterity saving throw or be knocked prone.
  • Magically charged shards of crystal fire from the crystals in the lair, striking up to two targets within 60 feet of the crystalline monolith. The crystalline monolith makes one ranged attack roll (+3 to hit) against each target. On a hit, the target takes 2 (1d4) piercing damage and 2 (1d4) psychic damage.

Crystalline Monolith

Huge aberration, lawful neutral
Armor Class 15 (natural armor)
Hit Points 123 (13d12 + 39)
Speed 0 ft., fly 30 ft. (hover)
STR DEX CON INT WIS CHA
14 (+2) 10 (+0) 16 (+3) 19 (+4) 17 (+3) 17 (+3)

Skills Arcana +7, History +7, Insight +6, Nature +7, Perception +6
Damage Resistances cold, fire
Damage Immunities poison
Condition Immunities blinded, paralyzed, petrified, poisoned
Senses blindsight 120 ft. (blind beyond this radius), passive Perception 16
Languages Deep Speech, Undercommon, telepathy 120 ft.
Challenge 7 (2,900 XP)

False Appearance. While the crystalline monolith remains motionless, it is indistinguishable from a giant crystal.

Magic Resistance. The crystalline monolith has advantage on saving throws against spells and other magical effects.

Powerful Mind. The crystalline monolith has advantage on Intelligence saving throws and ability checks.

Innate Spellcasting (Psionics). The crystalline monolith’s innate spellcasting ability is Intelligence (spell save DC 15). It can innately cast the following spells, requiring no components:
At will: detect magic, detect thoughts, mage hand, silent image
3/day each: clairvoyance, hypnotic pattern, stinking cloud, telekinesis
1/day each: confusion, dominate person, suggestion

Actions

Multiattack. The crystalline monolith makes two mind spear attacks. If both attacks hit a Large or smaller target, the target must succeed on a DC 14 Constitution saving throw or be restrained. The restrained creature must repeat the saving throw at the end of its next turn, becoming petrified on a failure or ending the effect on a success.

Slam. Melee Weapon Attack: +5 to hit, reach 10 ft., one target. Hit: 11 (2d8 + 2) bludgeoning damage.

Mind Spear. Ranged Spell Attack: +7 to hit, range 30 ft., one target. Hit: 14 (4d6) psychic damage.

Psychic Burst (Recharge 5-6). The crystalline monolith emits a burst of psychic energy in a 30-foot cone. Each creature in that area must succeed on a DC 15 Intelligence saving throw or take 28 (8d6) psychic damage and be stunned 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 crystalline monolith can take 3 legendary actions, choosing from one of the options below. Only one legendary action can be used at a time and only at the end of another creature’s turn. The crystalline monolith regains spent legendary actions at the start of its turn.

Detect. The crystalline monolith makes a Wisdom (Perception) check.

Teleport (Costs 2 Actions). The crystalline monolith magically teleports up to 120 feet to an unoccupied space it can see.

Cast a Spell (Costs 3 Actions). The crystalline monolith casts a spell from its
list of innate spells, using a daily use as normal.

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