I have been playing Corruption of Champion quite a lot lately, and I must say I love how some characters seem to be friendly or nice only to trick you and attract you to a trap, like Ceraph, or well, don't want to spoil it for those who haven't played it.
Another good example would be the "Apostitutes" from Dragon Age 2 (although that is a fight you can't really lose... I so wanted a bad ending there!) or Morinth in Mass Effect.
Now my question is, are there any other games with such kind of characters?