Apex Crystal Monster

Avoidance. If the Apex Crystal Monster t is subjected to an effect that allows it to make a saving throw to take only half damage, it instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.

Magic Resistance: Advantage on saving throws and effects from spells.

Reflective Carapace: When targeted by a spell -Anything- (even area of effect bullshit) Roll d6. 1-2 Spell goes through. 3-5 Unaffected. 6 Reflected back at caster.

Multiattack. The monster makes four attacks with its Crystalline tentacles.

Tentacle. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 8 (1d6 + 5) bludgeoning damage plus 3 (1d6) piercing damage.

Crystal Slash: Slash in a 10ft. 5ft wide line. DEX SAVE DC 17. 

Half on Success. 1d10 Radiant. 1d10 Psychic. 1d8 Slashing.

Judgement:

 Athletics Contest at creature within 5ft. Acrobatics can be used instead to dodge.

On failure, take 1d4+3 Piercing. And become Restrained on its back in a cage of crystal tentacles. 

At the End of your next turn, you can make a contested Athletics to Get out, or someone else can do it for you.

Every fail adds a Level of Crystallised 

Level 1 - Blinded and you Begin to suffocate as your head is covered in crystal.

Level 2 - You can make Checks at disadvantage to get out as your Limbs are Fully covered. 

Level 3 - You Are fully Petrified in Crystal. You Now have an AC of 20 and continue to suffocate- you also detach from the Monster.

While it restrains you this way, it cannot use its multi attack.

Bite: + 5 to hit. 5ft. On hit, take 1d6+5 Piercing.

Lightblade Parry: Add +3 AC to a melee attack within 10ft. if it would cause it to miss.