Forgiver Sign appears to heal enemies, or to do massive damage when damage should be zero.
Forgiver Sign Bug
The Bright Shield Rune's final spell, Forgiver Sign, heals the entire party up to 2,000 hit points of damage. The remaining value from the pool is then used to do damage to one selected enemy. So the spell can be used with an entirely healthy party to cause ~2,000 hit points of damage to an enemy, depending on enemy resistance and the Hero's affinity with the Rune. If your party needs 900 points of healing, 1,100 hit points would be used as base damage to one enemy.
There is a bug that arises when the party requires more than 2,000 hit points of healing. In that case, there are no points left to do damage, and the targeted enemy appears to receive massive damage (the number is usually white, indicating harm), or a massive heal. In either case, an extremely large number is overlaid, and the enemy does not die.
In reality, the enemy is neither harmed nor healed in this case. When Forgiver Sign's pool of hit points is depleted in the healing phase, the game sets the damage to -1. With this damage value, the enemy's hit points will not be updated, nor will the value be copied to the display buffer. However, the game still needs to display something for damage at the end of the animation, and it winds up retrieving garbage data.
What this means is the bug is entirely cosmetic. If you use Forgiver Sign against the Beast Rune's head, and an 18,376 point heal pops up, you have not actually undone all the damage you have dealt up to that point. It only means that the game expected to display something, and retrieved whatever value was left over from the last time that memory was used.
Modify the /CDROM/150_BPRG/BUFF0/BP0_FST.BIN
modules to set the damage to 0 instead of -1. The damage routines will be executed, but will do nothing, and the display buffer will be updated with a zero value.