Sonic 2 Armageddon Game is a ROM hack; 'Armageddon' suggests a drastic alteration to the original game's world and possibly gameplay. It might feature extensive level design changes, new enemies, and a significantly altered storyline.  The core gameplay could be vastly different. It was produced by the ROM hacking community; there is no association with Sega or Sonic Team.

Sonic 2 Armageddon Game

Sonic 2 Adventure Edition