Rare's Battletoads (1991) is two things at once: an impressive, funny, great-looking beat-'em-up, and one of the hardest games ever put on a cartridge.

The toads morph their limbs into giant boots, rams and horns for hits that pause the action for a frame or two while the sprite balloons to three times its size. That freeze is why the punches feel so good, and it's a trick Rare's artists used all over the game to make an 8-bit brawler read as cartoon slapstick.

The variety is the other surprise. Twelve stages and almost none of them play the same way. You brawl, you rappel down a shaft, you ride a snake, you outrun a giant ball down a corridor, you fight in a gravity-flipped tube. Rare kept changing the genre every few minutes, which is generous design and also the reason the difficulty curve is a cliff: you never get to be good at anything for long.

Then comes Level 3, the Turbo Tunnel. Hoverbikes at increasing speed down a track full of walls that arrive faster than reaction time allows. There is no reading it. You memorize the sequence or you don't pass, and it arrives a quarter of the way into the game. This is where the vast majority of players stopped, forever.

For the few who got past it there's a crueller surprise waiting. Stage 11, Clinger-Winger, has a bug in two-player mode that leaves the second player unable to steer, which means co-op cannot finish the game. Rare shipped it that way.

And the everyday co-op cruelty: you can hit your partner, and a clean boot to the head knocks out a chunk of their health. Friendships were tested. Controllers were thrown. Nobody who tried it forgot it.