"Barny says: I'm just batty about Butterbeer!"
-- Butterbeer advertisement (QA7)
In the United Kingdom, someone who is "batty" (as Barny the Fruitbat says he is about Butterbeer), is English slang for someone "crazy" or "mad, insane" (Lexico Oxford English Dictionary).
Lexicon list of Team mascots
From the Web
Harry Potter Wiki: Barny the Fruitbat
WizardingWorld (Pottermore) features: