User blog:NomadMusik/Can Sonic Do Everything? - The Hardest Achievement

I'm refering to the 360/PS3 Sonic games.

What do YOU think is the hardest achievement in a Sonic game? Personally, for me, it's "Can't Touch This" on Generations. That boss was pretty easy (even on hard), but trying to get this achievement was nigh-impossible. I barely got it today... after wasting 20-something lives.

So... what's the hardest achievement?