Originally Posted by C4PON3
Nice FAQ, but you do realise that you can't even play professional mode until you've done Veteran, right?
So the whole 'If I play proffesional mode will my achievements stack?' one doesn't make sense.
Neither does playing through veteran/professional after playing through on a lower difficulty setting.
Hate to be picky, but it might stop some new players getting confused when they can't find professional mode.
if you play co-op with someone who already has pro unlocked you can play with them & piggy back all of the difficulty achievements with them.