Anti-Magic Coating

You brandish the weapon used in the spell’s casting and make an attack with it against one creature within your branded weapons maximum range of feet from you. On a hit, the target suffers the weapon attack’s normal effects and then becomes enveloped in black aura tendrils of the user's antimagic until the start of your next turn. If the target attempts to cast a spell or use a magic based ability (cantrips count) before then, the target takes 1d10 damage, and the spell ends.

At 5th level, the attack deals an extra 1d10 damage to the target on a hit, and the penalty the target takes for casting is that the opponent's of said spell has advantage on the spell save. Damage roll increases by 1d10 and spell damage is reduced by the character (Whoever casted Anti-Magic Coat) STR modifier + 1d10 roll at 11th level (2d10 is 11th level damage roll) and again at 17th level (3d10).