Yeah, dying at any of the last few bosses in this game is beyond frustrating. The developers must have really wanted to discourage players at this final stretch of the game, since this setback only occurs in the final stage. At least you don’t have to refight any of the bosses that you manage to defeat, so as long as you can make it back and get to the current boss with good health and equipment, you’ll eventually beat the game. I should know, I’ve done it twice on a regular NES.