Sonic 2 Heros

My friend showed me this amazing rom hack that lets you play through Sonic 2 as Sonic, Knuckles, and Tails in Sonic Heros style.
It also adds some new items and abilities to the game, like elemental shields and double jumps.

The video comes in three parts, and just gets progressively more awesome.
Highly suggest at least giving the first a quick watch.

Info and download links here.