Occasionally assist characters' graphics will remain on the screen doing nothing. Happens with Hammer Bro. and the Rhino from Donkey Kong(I forgot the name) as well as a few others. Found this particularity in training where all I was doing was summoning a bunch of assist trophies and periodically in a match.

If you're jumping when a score is made in the Arena (as Sandbag, haven't tested with others), the sprite will continue to jump until the next round begins.

Replays aren't accurate to what actually happened in the game. Often times it gets the first portion right before something goes wrong where often times my character will merely jump to their death resulting in a CPU win. Likewise, assists and pokeballs in the replay don't generally match up with what happened in the actual gameplay as well as character colors and the endgame player statistics.