Tower of Druaga, arcade. And I won't even pretend I beat it fairly. This is, by far, the single most unfair game in the history of ever. You get three lives, no continues, most enemies kill you in one hit, controls are clunky, and there are 60 levels to get through, many of them full of mega-cheap teleport-spamming wizards. And just getting to level 60 isn't enough. Each level has a treasure that you need to reveal by doing something secret. Some are simple- kill a given enemy, walk over a given tile, etc. Others are absurd, how-the-hell-was-I-suppossed-to figure-that-out levels of insanity.
And the game tells you NOTHING about any of this- how to find the items, what they do, which are necessary, useful, or harmful- all this stuff has to be figured out by trial and error. Presumably the idea was that you trade stories with your friends and figure out the secrets as a group, but even so, the sheer density of impenetrable puzzles is insanity. I am fully prepared to call anybody who claims to have beaten this game fairly a liar. My best game playing fair was level 20 with 12 items. After that I found a walkthrough and started save-stating like a motherfucker. Ironically, playing the game this way was kind of fun.
Still a beast, though. Fucking wizards...