Originally Posted by nfntjy
About local coop achievements: if player 2 (earl) does something to earn an achievement, the achievement will not actually pop until player 1 (toejam) loses all his lives. I played as earl with my sister last week and did several of the achievements (santa, mailbox, cupid), but they did not pop until she got a game over. Completing the game may also allow the achievements to pop as well, but that's just a guess.
this was with player one signed into my Live account and player 2 not signed into an account.
When you say Player 2 wasn't signed in, what do you mean? AFAIK "Player 2" is always Earl in the game. Do you mean that the profile that wasn't signed in or guest started up the game and you joined locally AS Player 2?
I might try this out later and see what happens. if it's true then I guess if you used save states you may be able to simply kill off player 1 to unlock achievements and then simply reload (perhaps this could even be used near the end of the game - reloading so that each person can gain the achievement).
One more thing that I just thought of - has anyone that has tested/played the game through co-op started a Single Player game and THEN had Earl join? Does this make any difference whatsoever?
EDIT - I just tested out a 2 player local co-op game and I couldn't get the achievement(s) to unlock for Player 2/Earl even after Player 1 got a game over...