Breathless Assassin

Assassinate. During its first turn, the assassin has advantage on attack rolls against any creature that hasn't taken a turn. Any hit the assassin scores against a surprised creature is a critical hit.

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.

Sneak Attack. Once per turn, the assassin deals an extra 14 (4d6) damage when it hits a target with a weapon attack and has advantage on the attack roll, or when the target is within 5 feet of an ally of the assassin that isn't incapacitated and the assassin doesn't have disadvantage on the attack roll.

Stunning Strike. When the assassin hits another creature with a melee attack, it can spend 1 ki point to attempt a stunning strike. The target must succeed on a Constitution saving throw or be stunned until the end of the assassin's next turn.

Spellcasting. The assassin is a 7th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 14, +6 to hit with spell attacks). The mage has the following wizard spells prepared:

Cantrips (at will): fire bolt, light, mage hand, prestidigitation

1st level (4 slots): detect magic, mage armor, magic missile

2nd level (3 slots): misty step, silence,  darkness, hold person

3rd level (3 slots): counterspell

4th level (2 slots): dimension door

Multiattack. The assassin makes two attacks.

Shortsword. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) piercing damage, and the target must make a DC 15 Constitution saving throw, taking 24 (7d6) poison damage on a failed save, or half as much damage on a successful one.

Light Crossbow. Ranged Weapon Attack: +6 to hit, range 80/320 ft., one target. Hit: 7 (1d8 + 3) piercing damage, and the target must make a DC 15 Constitution saving throw, taking 24 (7d6) poison damage on a failed save, or half as much damage on a successful one.

Breathless Blast (Recharge 5-6). While holding it, you can use an action to cause a thin blue ray to streak from the mouth toward a creature it can see within 60 feet of you. The target must succeed on a DC 15 Constitution saving throw or be Paralyzed for 1 minute. At the end of each of the target's turns, it can repeat the saving throw, ending the effect on itself on a success.