A few days back Sega has released a remastered version of Sonic 2 for the mobile devices. This port of Sonic 2 claims to run at 60 FPS, it features knuckles as a playable character, online multi-player has been introduced, and last but not least a new level is featured in this port. It is the cancelled Hidden Palace Zone that never made it to the genesis release due to time constraints.

You can pick up this port for 2.99 on both Google play and Apple's App Store.

Source article:
Sonic 2 on iOS and Android