Ancient Crystal (5e Creature)
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Huge elemental (shardling), lawful good
Skills Arcana +14, History +14
Innate Spellcasting (Psionics). The ancient crystal's innate spellcasting ability is Intelligence (spell save DC 18, +10 to spell attacks). The ancient crystal can cast the following spells innately, requiring no material components:
At will: blur, guiding bolt, light, mage hand (the hand is invisible), meld into stone, minor illusion, tongues
Immutable Form. The ancient crystal is immune to any spell or effect that would alter its form, except for its Reshape.
Psionic Ward. The AC of the ancient crystal includes its Wisdom bonus.
Psionic Absorption. Whenever the ancient crystal is subjected to psychic damage, it takes no damage and instead regains a number of hit points equal to the psychic damage dealt.
Reshape. The ancient crystal can use its action to change its physical appearance into any form of its choice. The ancient crystal may not change its size or composition, so it may not become a Tiny crystal, but it may, for example, become a long chain of crystal that could fit into a space large enough for a Tiny creature.
Sense Thoughts. The ancient crystal senses thoughts within 120 feet of it at will. This trait otherwise works like the detect thoughts spell but isn't itself magical.
Multiattack. The ancient crystal makes three attacks.
Slash. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 14 (3d6 + 4) slashing damage.
The ancient crystal 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 ancient crystal regains spent legendary actions at the start of its turn.
Cast a Spell. The ancient crystal casts one spell that it can cast at will.
The most ancient of great crystals, ancient crystals are incredibly powerful psionics, the strongest of their kind.
Elemental Nature. An ancient crystal doesn't require air, food, drink, or sleep.