I don't know how I won, I guess I just did it how I would if it were me. Wish I could help, but I have zero clue how I succeeded. I suggest staying focused, and hiding. Choosing human, the safety of your friends (don't remember exact phrasing), and evolution should help.
Edit: If you are having trouble still, try qsave and qload, if you die you can always go back.
Also if you don't have 500 power, you probably won't win. I think I had 495 or 498, and the cutscenes just poked my power up to 500 when I wasn't looking. After the current progress available, you should have 512 or so (no spoilers).