Anti-magic skeleton

Ignis Fatis. The Anti-magic skeleton 19 charges, when a creature casts a spell with the Anti-magic skeleton as a target or with an area of effect that includes the Anti-magic skeleton, the skeleton can use their reaction to negate the casting of the spell, using an amount of charges equal to the spell's level, the spell slot is taken away but any material components that would be consumed won't be consumed though. Then the caster experiences an explosion dealing the same type of damage the spell would do, if the spell wouldn't do damage the type is fire. The amount of damage dealt to the caster is 1d6 per spell level negated, and only the caster takes damage from this explosion.

Multi-attack. The Anti-magic skeleton can make 2 attacks.

Anti-magic magic sword. Melee Weapon Attack: +6 to hit, reach 5 ft., 1 target. Hit: 15(2d6 + 3) slashing damage. A creature that is damaged by this sword that is concentrating on a spell must make their concentration check to keep concentration with disadvantage.

The Anti-magic skeleton has 3 legendary actions per round, and regains those legendary actions at the start of each of it's turns. The Anti-magic skeleton can use a legendary action in response to a certain action.

You're open (Costs 1 Action). When a creature casts a spell while you're engaged in combat you can make a melee attack against that creature.