So, I have the plan of a few cross universe episodes. Mainly its just Roo playing a prank with Max's summoning magic do he is another universe for 2-4 Chapters a universe. Here is the list of planned universes.
Supernatural
Dr. Who (10th or 11th)
Rencarnated as a Slime
And maybe a few more. Feel free to suggest any you would like to see. None of these will be story heavy at all, just thought it would be interesting