Originally Posted by
Anzai
Admittedly I haven't experimented much in recent memory, but from personal experience stuff that never seemed to work would be...
Vaan: Hand Bombs
Balthier: Spear
Fran: Axes
Basch: Ninja Sword
Ashe: Dagger
Penelo: Rod
Fun fact: Whenever I used Penelo in a Boss Fight she always ends up tanking for at least half the fight. Maybe I still haven't figured out how to properly utilize Decoy, but she deals too much Magick damage to keep the agro off of her. The funny part is she tanks well, even without a Main Gauche and Shield combo to bolster her block rates. This had always made her an amusing choice of party leader to have the Black Mage kiting a Wyrm or Esper around the arena letting the rest of the party backstab it with impunity.