This is a hacked version of Sonic the Hedgehog. The title character is replaced by his sidekick, Miles "Tails" Prower. The levels remain unchanged.
There is more than just an appearance change to this game. Tails' abilities remain intact. If you haven't seen Sonic the Hedgehog completed before, you may wish to do so before seeing what a character with flight and a spindash can accomplish.
There is also a run for a Knuckles hack of Sonic the Hedgehog, done by JXQ. It replaces Tails with Knuckles and flying with climbing and gliding.
This run is 2.73 seconds faster than the previous version. The improvements are mostly done in the Green Hill Zone, but also in the Spring Yard Zone.
Note: An IPS patch for the hack can be downloaded here. It must be patched to REV 00.