Monster is a fanmade Halloween Sing-a-ma-jig. He is dark blue, has the same shape of ears as the Lawn Green Sing-a-ma-jig, has black square eyes, a green nose, a blue mouth, wears a 2-holed shirt, has the same arm pose as the Snowman Sing-a-ma-jig (But Mirrored), has the same shape of feet as the midnight Sing-a-ma-jig, has the same voice as the Skeleton Sing-a-ma-jig , and sings ""Great Green Gobs of Greasy Grimy Gopher Guts"". He signs on, and signs off the same way as the Skeleton Sing-a-ma-jig, and enters song mode the same way as the midnight blue.
Monster blue sing a ma jig

This is what he looks like.