As so many others have observed, the ending spoils an already imperfect film. Overall, it was like Netflix said to Del Toro, “we really like what what you’ve done with the series and we know there is a fan base out there hungry for more but we’re not going to spend much on this effort and we certainly don’t need to waste money on writing. Splash a lot of bright colors on the screen and keep the action going and get it made.
Then the ending, it undoes everything. None of it really happened and the basic premise of Troll Hunter is undone as we start into an alternate time stream and reboot into what must be an alternate universe with alternate rules about how the Troll Hunter is chosen.