Sneak Attack. Once per round the Assassin Candyland extra 8D6 piercing damage 

Evasion. If the assassin is subjected to an effect that allows it to make a Dexterity saving throw to take only half damage, the assassin instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.

Assassin's eye. The Assassin has a Keen Eye for Vital points of Their target. Would the Assassin attacks in Target a 17 and up is considered a critical hit for them.

Protecting sword, Whenever Xavier  has a mind-controlled Creature or person within five feet of him. He can force them to jump in the way of an attack against him. The school block the attack in deal no damage to  Xavier

Multiattack. The Assassin will make three attacks, 1 with its dagger and 2 with its Bolter gun 

Claw. Melee Weapon Attack: +15 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 5) slashing damage. And Upon a hit  the person targeted must make a DC 15 Constitution saving throw if they fail they are considered poisoned and paralyzed.

Bolter gun. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 13 (6d4 + 5) slashing damage.