Mixels x Hey Arnold crossover: The Haunted Train
(The episode begins with an ominous vision of an old train in the dark with smoke all around it and ominous music plays and then slowly fades out and it shows an ice cream truck at night driving by and reveals that a hooded figure is holding a sack of ice cream and the street lamp shortens out and when it turns back on, the hooded coat was on the sidewalk and the mysterious figure jumps on a high building and reveals himself to be Mysto, and then he comes out of the darkness and kids from Mixopolis Middle School and the other Nindjas see him and cheer except for Booger and Camillot, who are bored. He then gives them ice cream.)
Mysto: Have you finished playing checkers, Booger and Camillot? (sits down with them on a crate.)
Booger: Yep. Mixy Eights, Slap Murp, Go Mix, Old Mix and every board game at school and a crossword puzzle too.
Camillot: We're bored, Mysto.
(A train horn is heard