Black Arts Beagle is a member of the Beagle Boys. He took magic lessons in an attempt to impress Ma Beagle. This came in handy during Scrooge McDuck's birthday party in 2018, when he disguised himself as the illusionist Nik Nokturne, and attempted to summon a ghost to get Scrooge's fortune.
Unfortunately for Black Arts, the ghost he summoned was Duckworth, who was more interested in freeing Scrooge from the box in which Black Arts had trapped him than stealing his fortune. Black Arts was chased out of the manor soon afterwards by a disguised Duckworth, who made him believe he'd accidentally summoned an eldritch demon, hopefully scaring Black Arts into quitting dark magic.
Black Arts Beagle may or may not be the same B. A. Beagle who wrote The Myth of the Shadow Realm, a book Webby Vanderquack read as part of her attempts to find a way to bring Lena De Spell back from the Shadow Realm.