Dying during Roy's Final Smash while not being the victim prevents respawning.

[TheDevicer]

Green Hill Zone. Roy final smashes someone. I don't recall who. Yoshi falls off the edge during the animation and dies. The victim of the smash loses their last stock. Yoshi now can't respawn. Roy suicides 3 times. Finally, yoshi spawns but the game ends.

 

[Xermo]

yeah, the bug has been circulating around a bit. Tested it yesterday and it works as such:
When Roy activates his final smash, whether it be on thin air (bug) or an opponent (only tested with cpus), those who are not caught in the move will remain in their previous action without being able to control themselves. As such, if Roy hits cpu 2 and cpu 3 is jumping, cpu 3 will continue to fly upwards until the move ends.
If an opponent dies that wasn't hit in the smash (Cpu 3 hitting the blastzone), they'll "freeze" and wont respawn until about 30 seconds later.