Yeah any move that cause multiple status ailments are generally just bad news in these games and Bad Breath is the poster child for that. So that also gets my vote
Would like to give an HM to a move I believe was called X-Zone in FF6. One time I was grinding a tower in the WoR (I forget its name) on the upper levels to get growth points for my characters to learn skills. I must have been dong this for about an hour or 2 and finished up and made my way to the exit. Only for an enemy on one of the lower floors to use that move and OHKO my entire party. Game Over, made me very unhappy (fyi there was no save points in that tower).
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Celtic FC - Come on you Bhoys in Green!
http://s22.postimg.org/552gnbb9d/S1_Ne2v_J.jpg