Sonic The Hedgehog 3 Complete is a ROM Hack. See ROM Hacks
Sonic The Hedgehog 3 Complete (often shortened down to Sonic 3 Complete) is a hack of the Sega Genesis/Mega Drive game Sonic The Hedgehog 3 & Knuckles. The hack was made to present the hacked game like it was originally intended to be, with some altered placements of levels and how it contains the zones and events from Sonic & Knuckles. In some way, it could be considered a G/MD port of Sonic & Knuckles Collection.
The game plays identically to Sonic 3 & Knuckles. The player can either play as Sonic, Tails or Knuckles (Sonic and Tails can be separate or partnered). Sonic can do an insta-shield attack when pressing the jump button on mid-air. Doing the same for Tails lets him fly, and Knuckles can glide and climb up walls.