Sonic 3 vs Sonic & Knuckles: What Is the Difference?

Sonic the Hedgehog 3 and Sonic & Knuckles are the two halves of one game. Sega planned a single adventure, released the first half as Sonic 3 in February 1994 and the second half as Sonic & Knuckles in October 1994. Plug Sonic 3 into the top of the Sonic & Knuckles cartridge and the two join into the complete game, Sonic 3 & Knuckles. Here is what each half contains, how they differ and how to tell which one you are playing, with Sonic & Knuckles playable on our Sonic & Knuckles page.

Why one game became two

Two problems pushed Sega to split the game. The first was time: Sonic 3 had to be in shops for a promotional deal with McDonald’s in the United States early in 1994. The second was memory: cartridges big enough for the whole adventure were expensive, and the planned game did not fit on one affordable chip. So the first six zones shipped as Sonic 3, and the team kept working on the rest.

The solution for joining them again was the lock-on cartridge. Sonic & Knuckles has a slot on top, and a game plugged into that slot runs through it.

Sonic 3 vs Sonic & Knuckles at a glance

The story runs straight from one to the other: Sonic 3 ends with Dr. Robotnik’s Death Egg falling back to Angel Island, and Sonic & Knuckles picks up the story on the island, starting in Mushroom Hill.

What lock-on does with other cartridges

• Sonic 3 on top: the full game, Sonic 3 & Knuckles, with all fourteen zones in a row, saving, Knuckles playable in the Sonic 3 zones, and the Super Emeralds that unlock Hyper Sonic.
• Sonic 2 on top: Knuckles in Sonic 2, the whole of Sonic 2 played with Knuckles’ gliding and climbing.
• Most other Mega Drive games on top: a “no way” screen that leads to Blue Sphere, an endless version of the special stage. The original Sonic the Hedgehog unlocks the full Blue Sphere game.

Playing as Knuckles

Knuckles is the reason Sonic & Knuckles exists as more than “part two”. In Sonic 3 he is the rival who keeps knocking Sonic down; here he becomes playable for the first time in the series. He jumps a little lower than Sonic but can glide by holding the jump button in the air, grab and climb walls he glides into, and break some walls that block Sonic. That opens different routes through every zone, and his story ends earlier, at Sky Sanctuary, while Sonic goes on to the Death Egg and, with all the emeralds, The Doomsday.

How to tell which game you are playing

Many websites and download lists label the Sonic & Knuckles cartridge as “Sonic 3”, and the other way round, because the two are so closely tied. The quickest check is the title screen: Sonic 3 shows Sonic and Tails with “Sonic the Hedgehog 3”, while Sonic & Knuckles shows Sonic and Knuckles with the red and blue “Sonic & Knuckles” logo and “© 1994 Sega”. The first zone gives it away too: Angel Island is Sonic 3, Mushroom Hill is Sonic & Knuckles.

We checked this the hard way: the file another site offered as “Sonic 3” turned out to be Sonic & Knuckles on its title screen, so our page carries the right name.

Tips for Sonic & Knuckles

• Spin dash everywhere. Hold down and press jump a few times, then let go of down. It gets you up slopes and through tight tunnels from a standstill.
• Touch every star post. They are your restart points when you lose a life.
• Look for giant rings. They hide off the main path and lead to the special stage, where turning all blue spheres red wins a Chaos Emerald.
• Use the shield moves. With a fire, water or lightning shield, Sonic’s second jump becomes a dash, a bounce or a double jump.
• Use save states. The standalone game cannot save, so save the state on our page before a hard boss.

Where to play

Sonic & Knuckles runs in the browser on our Sonic & Knuckles page, with keyboard, gamepad or an on-screen pad on phones, and downloads about 3.4 MB the first time. If you enjoy Mega Drive classics, Snow Bros from 1993 runs the same way.