The New Batman Adventures (1997)

S02E10 Beware the Creeper

Title: Beware the Creeper Plot: After encountering a bizarre concoction of chemicals, featuring the Joker's notorious laughing gas, uptight journalist Jack Ryder transforms into the maniacal Creeper. Driven by a desire for vengeance against the Joker, he finds himself grappling with an unexpected infatuation for Harley Quinn, complicating his mission.