This is an official version of Sonic the Hedgehog 2 with Sonic & Knuckles locked on it. Here, the title character is replaced by his rival, Knuckles, who has his signature ability of gliding and climbing carried over to this version. Other than that, the levels are unchanged. If you haven't seen Sonic the Hedgehog 2 completed before, you may wish to do so before seeing what a character with a spindash and gliding can accomplish.
ShiningProdigy9000 saves 17.5 seconds over the previous run through various stage improvements and optimizations.
For more Sonic the Hedgehog 2 tool-assisted speedruns, you can check out this page.
There are also alternate CamHack encodes that attempts to keep Knuckles visible on the screen as much as possible and over any sprite layers.