Anti-Mage Wasp Queen

Magic Weapons. The wasp's weapon attacks are magical.

Anti-Magic Carapace. The wasp is coated in a thick carapace that is extremely resistant to magic of all kinds. Saves against magical spells are taken at advantage. Any form of magical damage dealt to the wasp is halved. 

Multiattack. The wasp makes three attacks: one with its sting and two with its sword talons.

Sting. Melee Weapon Attack: +9 to hit, reach 5 ft., one creature. Hit: 9 (2d8 + 5) piercing damage plus 8 (2d6 + 5) poison damage, and the target must succeed on a DC 15 Constitution saving throw or be poisoned for 1 minute. While poisoned in this way, the target (when casting any magic) must also make a DC 15 constitution saving throw. On a failed save, the spell fails. When a target is concentrating on a spell, they have disadvantage to hold their concentration on a successful hit. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. 

Sword Talons. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 8) piercing damage.

Mage Slayer. When a creature within 5 feet of you casts a spell, you can use your reaction to make a melee weapon attack against that creature.

Legendary Resistance (3/Day). If the Wasp fails a saving throw, it can choose to succeed instead.