Publisher: Taito, Natsume
Released: N/A (unreleased prototype), Super Nintendo
The only publicly-known Lufia II/Estpolis Denki II prototype had an unfortunate accident that fortunately was fixable: The first dumper of the ROM accidentally damaged one of the chips during the dumping process, rendering the game unusable. Later on (after changing ownership), others were able to re-dump it and patch the damaged sections of the ROM with pieces from the retail version, or just plain ingenuity.
The Lufia II prototype contains many features in various stages of completion that didn't make it into the final build of the game. This includes an (extremely incomplete) area where your capsule monsters could've been pitted against others like Pokémon! It was very fortunate that the damage to the ROM was so minor, and that people worked so hard to restore it after the fact.