Invisible Billy Adventures is a deleted scene that appeared in asdfmovie: deleted scenes.
Plot[]
One of Billy's friends exclaims "Hey, Billy! Catch the frisbee!". He throws it to Billy, where a small splash of blood appears (presumably his neck was severed), followed by a rustling on the ground (Billy falling to the ground).
Billy's friend then worryingly exclaims "B-Billy?!"
Transcript[]
MALE SINGERS: ♪ Invisible Billy Ad-ventures! ♪
OFF-SCREEN MALE: Hey Billy, catch the frisbee!
(The frisbee is thrown and kills Billy, who then flops onto the floor)
OFF-SCREEN MALE: B-Billy?!
*static*