Several years after release, though, finding two fresh players would be a rare trick indeed.

Portal 2's co-op is strongest when neither of you know the answer: if your partner waits patiently for you, you feel like a moron if they don't, they'll be rushing you through all the discovery that makes the game great. The three-dimensional spatial thinking that makes the Portal series so addictive is only magnified when there's another friend getting stumped at the puzzles with you. As the two testing robots Atlas and P-Body, you and a friend get to explore the darker, more dangerous side of GlaDOS's testing routines-the stuff that's too dangerous for (non-protagonist) human testers.

There's no denying the raw quality of Portal 2's distinct co-op campaign. The digital remaster release includes 'D-T-D' (credited lyrics: Sakurai, music: Imai), but not 'Not T Dise' or 'Kirameki no Naka de'.Release Date: 2011 | Developer: Valve | Players: 2 | Steam The names of these hidden bonus tracks were only given in a magazine published at the time. On the originally released 1993 CD, after track ten it skips to track #75, titled 'Not T Dise', after that the CD skips to track #84, titled 'Kirameki no Naka de' and finally after that, it skips to track #93, titled 'D-T-D'.Ken Sakaguchi - cover art, graphic design.Hirohito Fujishima Katsumi Moriya - assistant engineers.Shigetoshi Naitoh Takahiro Uchida - engineer.Osamu Takagi Takafumi Muraki - executive producers.Hitoshi Hiruma - producer, recording, mixing.Kazutoshi Yokoyama - backing vocals on 'Dress' and 'Kirameki No Naka De'.

Hidehiko Hoshino - rhythm guitar, keyboards, synthesizers, backing vocals, piano.Hisashi Imai - lead guitar, backing vocals, lead vocals on 'Madman Blues'.

Buck tick darker than darkness