I'm not sure how they handle bombs, since certain moves only make sense given bomb timing and positioning. Also not sure how they handle moves that become impossible at the very top of the screen -- if line timings are different, the replay ends up trying move to a place that a real player actually can't get to.
Edit/Note: If you're playing someone live, it'll say so under your names -- one of you will have 'host' and the other 'live.'
It seems like the issue with blockbattle is that you might get dumped into a fresh lobby with no players yet, although active players are in other lobbies. Perhaps "Find Opponents" should always dump you in an active lobby and an option should be added to create a new lobby?