Dot.Hack Part 2: Mutation Cheats
Marlo: He will post a message on the board asking you to go to a dungeon. help him in defeating the monster at the bottom.
Moonstone: You should have found him in the previous dungeons. at a certain point he will send you an e-mail. Go were he asked and clear the dungeon.
Nuke Usugimaru: After reading his post on the board go to that location, then defeat the monster on B3 floor.
Rachel: After reading her post go to that location. Find the item she is looking for and trade items with the others on B1 floor.