Callidus Assassin
Medium Humanoid, Neutral

Armor Class 20
Hit Points 20d8+100 (190)
Speed 50'
Strength Dexterity Constitution Intelligence Wisdom Charisma
20 (+5) 30 (+10) 20 (+5) 18 (+4) 18 (+4) 26 (+8)

Saving Throws Dexterity +16, Intelligence +10, Wisdom +10
Skills Deception +20, Intimidation +14, Persuasion +20, Stealth +22, Acrobatics +22, perception +10
Damage Resistances Poison
Condition Immunity Poisoned
Senses Darkvision 120', Blindsight 10' Passive Perception 20
Languages Nearly Any
Challenge 19

Assassin's Sight Magical Darkness does not impede the Assassin's Darkvision.

Incredible Reflexes The Assassin has advantage on all saving throws, and on any saving throw that does half damage on a success, she instead takes no damage on a success and half on a failure. In addition, she is able to run up walls and across liquids as if they were flat, solid ground

Polymorphine Suit The Assassin can transform into any small or medium creature. She gains the appearance of the creature, but none of its abilities. When transformed, she has advantage on checks made to conceal her true identity.

Sneak Attack Once per turn, when attacking a creature with advantage or with an ally adjacent, the Callidus can deal an extra 35 (10d6) damage.

Actions

Extra Attack (3) The Callidus Assassin makes four attacks or other attack actions.

Phase Sword Melee Weapon Attack: +16 to hit with advantage, reach 5', one target. Hit: 15 (2d4+10) phasing damage. Phasing damage ignores all resistances.

Poisoned Blades Melee Weapon Attack: +16 to hit, reach 5', one target. Hit: 15 (2d4+10) slashing damage and 21 (6d6) poison damage.

Neural Shredder Ranged Cone Attack: 25' long and 15' wide cone, DC 24 Dexterity Saving throw. On a failure, take 22 (4d10) psychic damage and make a second Wisdom saving throw, DC 22. On a failure, become paralyzed for one minute, repeating the saving throw at the end of each of your turns. On a success, take half damage and you do not have to make a Wisdom Saving throw.

Bonus Actions

Cunning Action The Callidus takes the Dash, Dodge, Disengage, or Hide action.

Attack The Callidus makes a single attack.



CR discussion.

Defensively, she's CR 8 by HP, then bumped up by 2 for an AC 4 points higher. Thanks to three good saves, that goes up one more, for 11.

Offensively, she's at 179 damage per turn (Poisoned Sword, four hits, and one sneak attack) with some decent AoE. That's CR 23, but her attack value bumps that up to to 25, as does the save DC. Since her Phase Sword has advantage, I'll bump it up once more for 26.

26+11=37, 37/2=18.5, rounded up is 19. CR 19 sounds good to me.