[Warning: Spoliers]
UDM (Upside-Down Magic) is captivating.
I mean, come on. We have a compelling plot, first. Instead of learning to use magic the normal way ("The Sage Way") the kids with the Upside-Down Magic (the UDM's) use their magic for good purposes and prove Sage Academy wrong by the end of the film.
Then we have the young cast. Each and every one of them is so good at their roles, and they outshine the adults at times.