Malboro from FFVIII, Yan from FFIX...and basically, all those one-hit monsters from FFVII. One-hit is like they toss you out of the battlefield for no apparent reason at all and only 1 or 2 characters are left or is/are killed; similar to the Yan's Snort and Comet.

Malboro from FFVII's pretty manageable if you have a Ribbon equipped. The Malboro from FFVIII is the WORST. I still have to see the Great Malboro, though.

Life is short.
Let's all grab a BEER~~~!!!