Magic Resistance. The wretched have an advantage against saving throws against spells and other magical effects.

Mana Sense. The wretched can cast detect magic at will (permanently active). As a bonus action, the wretched can move up to its speed toward a hostile creature that it can sense by detect magic spell. 

Mana Feast. When damage dealt by the wretched breaks creature's concentration on a spell, the wreatched absorbs the scattered energy, gaining 4 (1d6+1) temporary hit points. 

Multiattack. The wretched makes two attacks. 

Scimitar. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) slashing damage.

Claws. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 5 (1d4 + 3) slashing damage.

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