To everyone still playing this:
If you play every map in a
private match all by yourself and then win a match on any of the maps in a non private one, you can unlock the achievement.
Solo part-So setup a private match
-ADAM grab as the gamemode as this takes little over 3 minutes
-Launch the game by yourself
-Grab the little sister until you win (3 min)
-Go down the list of all the DLC maps (described in the other guides)
Non solo part-Play a NON-private match on a DLC map and Win Win it (tie win doesn't count)
-Achievement
S unlocked
this also unlocks this achievement:
The Aqua Incognita achievement in BioShock 2 worth 60 pointsPlay at least one non-private match on each downloadable content map. Extra info-If want to boost this set it up with 4 people and switch holding the little sister in "adam grab". You might get 'randoms' but you should be able to win very quickly anyway. If you abhore that then set it up with 6, just make sure
everyone did the Solo part first-This also works for the regular maps, but you'll have to win on a regular map to unlock that achievement, it also requires you to apply the solo part on the regular maps first as well
-I do not want to take credit for inventing this. This info was passed on to me through a friend of a boosting partner