VIDEOS:
Favors for Joker & The Devil
The second to last episode of The Cuphead Show has a few references to Joker's Favor from Batman: The Animated Series, namely a character (Charlie Collins and Ms. Chalice) has to do a favor for a villain (Joker and The Devil) at a later date, unaware they're hiding an agenda behind it...
Example of:
Shout-Out