Originally Posted by Flibbity Floid
Live Co-op disables achievements
Achievements are obtainable in 2 player Local Game since that was the premise of the original game.
I quickly ran a test just now and found that to be only half right. Player 1/ToeJam can earn achievements (tested this by restarting with different profiles and on 2 seperate achievements) but Earl cannot. This was also the case with TJ&E2.
I can edit the guide to reflect this, but as far as general "achievement hunting" goes, it's rather impractical to play 8 seperate playthrough's (assuming completion achievements unlock). Especially with savestates at your disposal.