Weigraf And Velius: Two Birds With One Stone:

When you encounter Weigraf for the last time(just before he becomes Velius) you cankill him easily by following these instructions:

Make sure Ramza is a Squire with two sword ability or a Ninja with HP Restore and the support skill Guts equipped.

When you start the battle it's just you (Ramza) and Weigraff. Don't attack him, instead keep away from him and use Yell and Accumilate repeatedly when it's your turn.

Eventualy this will raise your speed and level high enough that you don't have to worry about his Lightning Stab or Earth Slash attack.

When you are getting 3 to 4 consecutive turns in a row (Check the AT list) wait until the beginning of the next cycle then attack. Your two-sword ability should kill Weigraff in one turn and Velius will be dispatched before anyone else even gets a turn.

This should make what was the hardest battle in the game quite simple. Good luck!