Knuckles the Echidna in Sonic the Hedgehog 2

Knuckles the Echidna in Sonic the Hedgehog 2 (or simply Knuckles in Sonic 2) is a platform video game which is the result of locking-on Sonic & Knuckles with Sonic the Hedgehog 2 using the former cartridge's unique "lock-on" technology. As the name suggests, this game is essentially identical to Sonic the Hedgehog 2 with the exception of Knuckles the Echidna starring as the main playable character, and Sonic the Hedgehog and Miles "Tails" Prower are not playable in the game.