Sonic & Knuckles

What if a cartridge weren't just a box with a game, but a key that unlocks other games? Sonic & Knuckles on the Mega Drive became famous not only as a first-rate platformer but also thanks to the ingenious "lock-on" technology that turned it into one of the most inventive pieces of the era of eight-bit and sixteen-bit legend.

At first glance it is a classic Sonic as you know it: speed, loops, springs and iconic music that burrows into your head. But it added the character of Knuckles, a burly echidna who can glide through the air and climb walls, opening up entirely new paths through the levels and changing both the pace and the approach to the game.

The real magic, however, hides on the back of the cartridge. When you slot Sonic 3 into Sonic & Knuckles, both games combine into one giant campaign — and it is precisely this combination, often described as the peak of the whole series, that offers the best of both worlds. You can also "lock on" older instalments and play as Knuckles where he wasn't before. For its time it was a small technical miracle.

The levels of Sonic & Knuckles itself rank among the best designed in the series: sprawling, full of hidden paths and tuned to reward both a fast run-through and careful exploration. Visually and sonically it is the peak of what the Mega Drive could squeeze out, and the boss battles have the necessary dose of grandeur.

Thanks to the linking trick and the quality of the game itself, Sonic & Knuckles earned a reputation as one of the console's cleverest and most beloved titles. It is a game that showed hardware, too, can be part of a creative idea.

Why play it: A top-tier Sonic platformer with an ingenious lock-on cartridge that combines it with Sonic 3 into the crowning experience of the whole series.