The Grim Adventures of Billy and Mandy (2001)

S4E12 Scythe for Sale

In an effort to fund his purchase of Sea-Critters, Billy organizes a garage sale, where he unwittingly sells Grim's scythe to Irwin for a mere two cents. Harnessing the scythe’s formidable magic, Irwin manages to hypnotize Mandy and whisk her away on a date. Meanwhile, Billy and Grim scramble to retrieve the scythe. Once they succeed, Mandy breaks free from the spell. As a consequence for his actions, Irwin is shrunk down and transformed into a tiny sea-critter, destined to live in Billy's fish bowl.