Use arrow keys to move around. Try to dodge Sonic, Sonic.EXE, and Tails. You can buy Metal Sonic for 30 coins, or a speed and jump boost for 10 coins. You get 5 more coins each time you dodge Sonic, or Knuckles. Remember Sonic, Sonic.EXE, Knuckles and Tails hurt you if they touch you.
Credit to @shark-survivor for original. I suggest you go play the original first because @shark-survivor spent a lot of time on it and it's getting updated frequently!
