Skarr ending up betraying Bun-Bun, whom he was pretending to betray Underfist for (he spent most of the special hating the idea of the Underfist team, so his betrayal of them seemed so convincing.)
In this one from Big Boogie Adventure, when a giant octopus eats Billy alive, Mandy didn't seem to worry.....until later:
Mandy: (with an unsure look) We don't need Billy anyway....right?
Grim: (shrugs)
Irwin: We need Billy!! (cries)
Mandy: (hits Irwin with an arm for paddle) Billy is....always fine...(looks down to the river and quickily wipes a tear)
How about the ending to "aren't you chupacabra to see me?
billy: (tearing up) I-I love you, Daisy!
daisy the chupacabra: (fading) I love you too billy (vanishes)
Billy: NOOOOO!!!
everything that follows, however, is hilarious :D
Billy finally accepting Jeff as his son in Wrath of the Spider Queen.