Looking for these original famicom carts: Holy Diver and Crisis Force.
I would really like both CIB but would consider lose carts if the price is right.
I would try and just get a holy diver cart at first. Its so insanely hard you will hate yourself for spending so much money. Unless you haue a retron5. Save states help alot!
Holy Diver is pretty much the only game that I hear being labeled as insanely hard, and I actually agree with it. More lethal randomness than pretty much any other game out there I can imagine. The only way I can 1CC it consistently is by picking up every 1-up available to maximize my chances of getting a good pattern in one of the 'nightmare rooms'.
Theres a cheat to get you approx 100 lives. But it just means when you die you only restart the section not the level. It helps but still very hard. Level 4 boss and last boss approach make you cry.
It's a good game, one of the first I picked up when delving into Famicom exclusive titles. Unfortunately I don't have an extra to sell, aside from a bootleg cart of it (and the bootleg is probably rarer than the legit cart).
The game is fun, but quite difficult.
I have a loose copy I might be willing to part with for the right price. I've tried playing it before and the furthest I could get was level 3. :'(