Dios is a sidescrolling action adventure game that has some strange behaviour with its weapons. Each character can get three weapons, and for all of them the first and third weapon's shots pass through enemies. Each character's second weapon does not, making them universally a downgrade from the default for no apparent reason. By changing a single byte at address #3814 from #C0 to #C9, the second weapon will pass through enemies like the others, making it a worthwhile upgrade.
Now that a dump of the CD version of Dios is available, I was able to compare the two. As it turns out, the CD version behaves exactly the opposite, so the second weapon pierces but the first and third do not. The subroutine is the same in both versions, just at a slightly different offset. Making the same change would make it so that none of the weapons pierce, but changing #3826 from #C0 to #00 instead will have the intended effect.
The disk image of Tug of War that is available online may be a bad dump, or it may be broken in the original, but regardless there is a bug which freezes the game in an endless loop after beating the last boss. By changing a single byte at address #3999 from #FE to #00, the ending of the game can be viewed normally.