Just want to give you guys a warning before starting the game. The difficulty the host chooses is not the difficulty that the 2nd player is going to have, and this is confusing because as the 2nd player, you don't get to choose a difficulty before entering a game. What you have to do is first start up a campaign and then select your difficulty, then quit out when you get the chance. Now your difficulty will be whatever you last chose. This is ass backwards and completely screwed me on 3 chapters. I was playing on normal as the 2nd player and my buddy was on professional as host, and there's no way to tell unless you go into your records and check.
Also, joining in someones game, even if they just started the level, will not count for you. You need to join while the host is in the lobby. Leaving a game and rejoining still falls under not counting for you
Also, joining in someones game, even if they just started the level, will not count for you. You need to join while the host is in the lobby. Leaving a game and rejoining still falls under not counting for you