Thread:SynfulBlood/@comment-24527356-20140628033148/@comment-8485155-20140628035742

Due to the nature of these moves, they would only be usable once. Furthermore, if Perish Song faints the final Pokemon of either trainer, the user of Perish Song is counted as the winner. However, if the user faints beforehand, the opponent wins.

As for Destiny Bond, the user can only win by using it if the Trainer has other pokemon remaining. If used between the final pokemon of either Trainer, the opponent still wins if they faint the user.