Before Sonic the Hedgehog came along and sold millions of machines for Sega, the MegaDrive's main selling point was its ability to host arcade conversions that were supposedly indistinguishable from the coin operated original. There were a few failures, but some very creditable efforts. But supreme among them was GnG. An arcade monster from Capcom, for a period on import it was then the most expensive MegaDrive game yet seen (weighing in at £44.99 in 1989 money). Probably because the cartridge was a whopping six megabits, which is a mammoth 768 kilobytes to you and me. Small, but as it turned out, perfectly formed.
Yes, the game is hard. Indeed, in the canon of hard retro games it can often find a citation or two. But what makes it particularly fiendish is a little trick Capcom include in the franchise's games. Picture the scene. Your armour is rusty with the ichor of demons. In each of the lands behind you, corpses of dead bosses and assorted abominations are attracting flies and carrion eaters. You fling the final daggers into the huge fly thing waiting at the end of the game. It explodes like so many others, the gates open and ... you're sent right back to the beginning of the first level. Yes indeedy, you have to go through the game twice to complete it. No, that's not annoying at all. The in-game narrative justifies it in terms of having to backtrack to acquire a weapon that can slay Loki - the wonderfully named Psycho Cannon. In truth, it's a fancy ball of blue lightning, but to have to go through an already tough game again is proper trolling.
Ghouls 'n Ghosts was about as scary as games got in the late 1980s. But it also pulls the trick of binding existential dread up with rock solid gameplay. Terrifying.