>>I've been looking through stuff in-game, and I can't find anything that actually describes what Trothfang looks like. I know there's a three-headed statue of him in the True Path tent, but does he normally have three heads? Is he human-looking, or something else?

Keep in mind that other than the racial patrons, most gods are rarely depicted in a consistent manner in game and don't have 'normal' forms. That said, you're right that Trothfang doesn't have many depictions around, and they mostly either involve centaurs or simply mention a "wild-eyed man". Here's a couple:

>A large humanoid figure with enormous claws stands amidst the smouldering remains of a Dragon Priest encampment. Blood drips from the corners of its mouth, which are drawn up in a triumphant smile.

>The red-marbled dark mineral depicts, with expert incision, the gory scene of a wild-eyed man plunging a spear into the arched back of his startled victim. In the background, a rampant centaur prances amid the ruins of a building.

~Aeth

>>I thought Trothfang's "form" Was the Centaur?

It's entirely possible that centaur is Trothfang's most preferred form since it's the only divine symbol that could also be considered a sentient race, but generally gods don't manifest in the form of their symbol animals themselves. Those usually appear as the gods' supreme servants; our commune quests are a prime example to this. However, there are also cases like the book "Lightning in the Dark" of Theren cleric shop where Huldah directly appears as a weasel.

~Aeth