Now that the dust has settled here, let me try a couple of thoughts.
@Velderan - I think it's fair to say that the gods are not allowed to directly intervene. Yes, you have avatars like Fizban or Astinus (sorry, dunno about Dougan, after my time) that appear in the story, sometimes parceling out a bit of exposition or comedic relief, but, at no point are they directly doing anything. They advise, they talk, but, they'd don't act. Which seems to be a fairly consistent thing in the series and yes, the Green Gemstone Man is what's preventing Takhisis from actually physically coming into Krynn. IIRC, though, it wasn't as an avatar - Takhisis wanted to actually directly manifest on Krynn. But, I'm very willing to be proven wrong there, it's been a while.