I was thinking recently and I realized I never got around to watching the short from the Season 5 DVD about Cruella meeting Mordred in the Underworld. I managed to find a good quality video from it on YouTube ( https://youtu.be/sxFEbBynU4A ). I'm assuming that this can be considered canon but maybe I'm wrong. Should we make a page for this somewhere on the wiki?
I think we are waiting for confirmation, but I take it as canon. They made sure to set it 50 years in the future, so it won't interfere with anything, so long as they leave Cruella in the Underworld and leave Arthur there as its ruler.