There's no "proper" werewolf form, the one in the event is just a specific Wolf-morph build. You can apply it by manually by pressing F12, opening the web console while in-game and typing this :
Code:
Scenes.Halloween.HW = new Halloween();
Scenes.Halloween.WerewolfTF();
Note that whatever equipment weapon and armor you're wearing at the time will be destroyed and replaced by a Werewolf hide and Werewolf claws, respectively, which have 0 ATK and DEF (but +2 static generation and +2 back scratching power), so you'll want to swap those out.
The knot you get recieves an invalid value when you do that, though, which means the game won't let you save (not that this is a problem per se, since you were never supposed to be able to save like this). You can fix that by resetting the knot like this :
Code:
TF.ItemEffects.SetKnot(player, {value: true});
Frankly, while others have said the opposite, there aren't really any good ways to get an actual wolf-morph. Lobos, Canis and Vulpinix all tend to give you a canine-morph character, but while I'd never noticed, it's true how none of them ever actually give you fur (which would appear as SetBody).