I've been playing this game on and off since Alpha, but I finally just beat Hard Purist Gaan-Telet today.
The only problem is, I didn't even know how to GET to Gaan-Telet for months, figuring it must be after unlocking all the monster classes or something like that. I ended up unlocking two monster classes before I even unlocked Gaan-Telet! I ended up, in frustration, looking it up on the wiki, discovering that I needed every trophy (I was missing two).
If I hadn't looked it up out of game, I'm not sure I would have ever unlocked it; the two trophies I was missing were the nose ring and the AA helm, and I'd always kill Rex/The Indomitable first.
Did I miss something that told me to get all the trophies in order to beat the game? I've been playing Beta DD on and off for a very long time, so I might have just forgotten something. In any case, I think there should be more of an emphasis on getting all the different types of trophies, maybe some sort of hint on the taxidermist screen?
That being said, I absolutely adore this game, and I'm glad to have finally beaten it! Now I just have to unlock the Gorgon...