Great game, I'm enjoying playing it so far !
Unfortunately, I found a bug that erased my save data. it append when i turned off my Game Boy while playing the first level of the mines, after the Doggo checkpoint. (I think its not a problem with my cartridge, because before everything works great : i had a save data that i use to continue the adventure between each game session.)
Another thing: I don't know if this is a bug or not, but isn't that 000 supposed to be replaced by the player's score? I've killed all the enemies, collected all the coins, and I think I've found all the secret doors.
i play on an unmodded Gameboy Color with the game on a bootleg cart flashed by the JoeyJr from Bennvenn. (I use this cart for long now and its my fist save bug i encounter with. ) Also This is not a dead battery fault bc I played after the incident and i was able to save and load my new save without any problems.