Bassbass Wihouveberry is a half-elf wandering bard encountered by the Dragon Friends in Season 4. She performed a song for faerie queen Titania as a gift from her husband Oberon, but he was almost immediately sucked into a shadow portal, which led to the arrest of the Dragon Friends and Wihouveberry.
Wihouveberry plays the bass guitar in a band called Just Me, which is just her. She is very proud of her mother, a human vegan chef named Guitarguitar Wihouveberry; her father, however, is distant and shows little interest in her.
Once, after a particularly lackluster gig, a creepy child that she sees only at night gifted her with a powerful magical necklace that improves her singing abilities (and beauty) but forces her to tell the truth while wearing it. It also has the ability to absorb magical energy from other sources touched by the wearer, but must then store the absorbed energy within itself, potentially overloading and creating unpredictable effects.
Her bass guitar can transform into a deadly crossbow at a moment's notice.
Ensorcelled revealed that Bassbass is in fact the goddess Mystra trapped in a human form by a ritual performed by Freezo, and her mortal memories are false. Mystra, the second deity of magic in the classic D&D universe, is responsible for the creation of the rules for mortal spellcasting (Mystra's Ban is the in-character reason for the existence of spell slots, limited levels, and casting specific times). Her canonical background also mentions that she became extremely jaded in her later life as a result of being the target of the plans of every random being who wanted more power.
A Very D&D Stream revealed that Bassbass' identity as Mystra was a late change to the campaign, in part because of its appropriateness to the lyrics of Tiny Bud. Originally, Hyperion Max was going to be Mystra's incarnation.