All versions of the original retail release of Phantasy Star IV had one particularly nasty bug: when you leveled your party to 99 (the maximum), character stats would be applied incorrectly. Many stats were reduced or swapped between characters, and several attack skills could be wiped from your characters' memory. Furthermore, the Japanese version had another bug: when Chaz (Rudy) learns Megid, it replaces Nazan. This romhack is a simple patch that fixes both of these bugs.
Seth's stats and skillset still suffer from the level 99 bug. However, considering the minor role in which he plays in the game, this should not be of much concern. Leveling Seth to 99 does not affect any other characters.RHDN Phantasy Star IV Bug Fix PageRelevant Link: