Calcinor

Reflective Crystals. Any time the calcinor is targeted by Magic Missile, a line spell, or a spell with a ranged spell attack, roll a d6. On a 1-4, the spell acts as normal. On 5-6, the calcinor is unaffected, and the effect is reflected back at the caster as though it originated from the calcinor, turning the caster into the target.

Shatter. When the calcinor takes bludgeoning damage, a spray of crystals bursts from its body. Each creature within 5ft of the calcinor makes a DC 15 Dexterity save or takes 11 (2d10) slashing damage on a failure or half as much on a success.

Spell Absorption. Anytime the calcinor succeeds on a save against the spell, it absorbs the spell's power into its crystals. It becomes unaffected by the spell, and the spell's power is absorbed for 24 hours. A spellcaster can purposefully cast spells to be absorbed by the calcinor to store its spells. The calcinor can use the spells via its Crystal Growth action, and the spells burst forth if the calcinor dies via its Spell Stored Death trait.

Spell Stored Death. If the calcinor dies, all absorbed spells burst forth from its crystals, targeting the creature that killed it as though the spells originated from the calcinor. The spell uses the spell save DCs and spell attack rolls of the original caster.

Sunlight Sensitivity. While in sunlight, the calcinor has disadvantage on Perception checks that rely on sight.

Tunneler. The calcinor can burrow through solid rock at half its burrow speed and leaves a 5ft wide tunnel in its wake.

Multiattack. The calcinor makes one Crystalline Bite and two Energy Burst attacks.

Crystalline Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 16 (2d12 + 3) piercing damage. 

Energy Burst. Melee/RangedWeapon Attack: +7 to hit, reach 5ft/range 120 ft., one target. Hit: 9 (1d10 + 4) radiant damage.

Crystal Growth (Recharge 5-6). The calcinor causes crystals to sprout from a point on a solid surface it can see within 60ft of it in a 15ft radius. Each creature in this area makes a DC 15 Dexterity save, taking 35 (6d10) piercing damage on a failed save or half as much on a success. The area becomes difficult terrain. The crystals create an area of dim light in their area and extend 5ft beyond.

Crystalline Spell. The calcinor casts a spell at its disposal owed to its Spell Storing trait from the area created by its Crystal Growth as an action, using the center of the growth as the origin point of the spell and using the spell save DC and attack rolls of the original caster.