Legendary Achievement in FIFA 12
Win a game vs. the CPU on legendary difficulty against a club of the same or higher star level
How to unlock Legendary
Like Riding Bikes, this one seems hard but is very simple. Set up a match against a club of the same or higher star level, then go to the Settings. The final Settings tab influences your opponent, so set everything positive to zero and everything negative to 100.
Next, go to the 6th Settings tab, which influences your team. Set everything positive to 100 and everything negative to zero. Now the match will be a walk in the park. I did this as Barcelona against Real Madrid and won 32-0.
If you want to do it the hard way, start up any match on Legendary difficulty against a club rated the same or higher and make sure you win.