The Grim Adventures of Billy and Mandy: Duck!/Aren't You Chupacabra to See Me?

"Duck!" An invisible duck that only Grim can see terrorizes him by making everyone think Grim is passing gas. But when the duck starts to terrorize Mandy, it meets its match."Aren't You Chupacabra to See Me?" Billy's new best friend starts to suck the life out of him.