This was something I discovered looking through my achievement list over the weekend, and comparing it to the achievement list on xbox360achievements.org - It turns out that, for whatever reason, the achievement PLANET WHISP - Restored! hasn't unlocked, when I know fair well that I've done what the achievement needs me to do (complete Acts 1& 2 of Planet Whisp) and have actually beaten the game. The other Achievement I'm currently missing is Can't Touch This which involves beating the Final Boss without taking a hit.
The only thing I can think of doing in order to get this is to start a New Game, but since I've managed to get everything, I'm concerned that starting a new game will erase all the other things i've managed to get (all the music, artwork, etc. ) So I'm probably going to have to back up my original save somehow.
Also, if you're interested: to get the Eggman Costume for your Avatar, beat the Rivals, Bosses AND Final Boss on Hard Mode. Rank doesn't matter.
Any advice on the matter would be great, yo.
