If you slow down and look at Min Min's Final Smash (video) frame by frame, it's easy to spot that all the other ARMS characters are just 2D sprites. No doubt here.
However, in the final part of the Final Smash, you can observe that the ARMS gloves are 3D and some even have a curve.
Are these "hands" actual 3D models being rendered real-time in Smash Ultimate? or is the sequence pre-rendered and layered on top of and beneath the player?