Voidshot

Ammunition (arrow or bolt), very rare
  This jagged black, glass arrowhead drinks in the light and seems lit as if with an unholy nimbus. After the arrow is fired, roll a d4. On a 1 it shatters and can’t be used again.
  Spelldrain. When you fire this ammunition and hit a target or surface, it generates a 20-foot sphere of dim antimagic for 1 minute. Each creature within the sphere has advantage on saving throws against spells and magical effects. Each creature that tries to cast a spell whilst in the sphere must make a DC 15 check using its spellcasting ability. On a failure, it fails to cast the spell, and the spell slot is absorbed by the black hole. On a success, it casts the spell as normal.