Ultimate Flash Sonic
From Sonic Retro
Ultimate Flash Sonic is an online flash game by Menace.ch. It is based on Sonic Advance 2, with the same music, characters, and levels. The game uses passwords to continue your progress after exiting.
Playable from Start
Tips for bosses
Egg Spinner: before the pinch mode, just hit him when the ball retracts backwards. At the pinch mode, follow the ball from behind and hit him the moment it's possible then pull back right afterwards to prevent the character from getting hit. Note that the pinch mode comes after 5 hits instead of 4.
Egg Bomber: for flying characters, the boss fight is much easier. Just fly to the other side of Eggman and jump to hit him right after he releases the bomb. Because that the physics are too simple, you simply get knocked to the side you're supposed to be on. With other characters, you have to carefully move to the correct position to just hit him and not get touched by the bomb.
If you complete the game, You will get a cheat and level select for the character you won as. Here's a list of the cheats:
If you input the code 595313131313131 (595 then six 31s) in the passwords, you can unlock everything. Inputting "dennis_gid" (case-insensitive, but without quotation marks) in the passwords, you'll unlock an easter egg - many "dennis_gid" texts flying over the screen.