Before you think: “PORTAL 2 HAS TWO ALTERNATE ENDINGS! OH MY GOD!”… no. What this means is that the single player and co-op have their own ending sequences, both with their own “surprise”.
“Both sets of credits [will feature something special], because we’ve got two credits,” Faliszek told VG247.
“So we had to do something twice as amazing. The cool thing is that we’ll make sure that the game doesn’t get too difficult. It’s more complex, but it’s never so difficult that you can’t solve it. You’ll get to the endings. We’d hate to think that people would only watch the endings on YouTube.
“It’s scary actually – the ending to Portal has over 5 million hits on YouTube.”
If you remember, the surprise at the end of Portal was the song, “Still Alive”, written by the fantastic Jonathan Coulton, and most likely one of the surprises is another song written by Jonathan.