For example, if my friend hosts a game and I join it and we go through the entirety of Act I, will I have to beat Act I all over again once I leave the co-op session?

2 Answers 2


While in CO-OP.

  • You gain achievements for co-op and for single.
  • You quest log count for co-op and for single.

So you gain more achievements playing as a group than solo. You don't lose nothing. But remember monsters get 75% more health for each player in the party.

About the quest progress.

  • You are starting ACT III quest 1
  • Your friend is starting ACT III quest 4
  • You jump in your friend game and finish ACT III with him

You'll be able to start all quest beyond 4 and the first quest in ACT III. But You'll need to complete the quests 1, 2 and 3 from ACT III.

  • Interestingly this absolutely did not work for me and another player the other day, we joined a mates campaign who was one mission behind us, we all completed act 1 and then when we finished for the night, logged in the next day, my campaign was back to where i was before i joined his game, and so was the other guy i joined the game with... bug?
    – user25493
    May 17, 2012 at 9:35
  • @Ben You probably have to select new quest to start your campaign from that point (and effectively skip in zour campaign what you have playd in MultiPlayer)
    – Hurda
    May 17, 2012 at 9:38

You won't have to redo the act. Every quest your character completes is completed both when playing with, and without, friends.

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