My Werewolves Are Different

I'm working on a setting for my Mutants And Masterminds group where the characters are primarily werewolves (no, it's not a Fur Against Fang setup, so don't ask). Here's what I've got so far:

The characters are able to assume both a regular wolf form, and a "hybrid" (i.e., Hollywood Werewolf) form. However, they choose a preferred form, with the following effects:

• FENRIS: Essentially a dire wolf. The humanoid version is bigger than their regular selves (think of how Colossus' body changes in metal form, in terms of scale). They're vulnerable to cold-iron.
• HYBRID: Basically a gorilla with a wolves' head and claws. The normal wolf form is slightly larger than a regular wolf. Hybrids have the classic silver weakness.

Those who come by their transformations naturally (i.e., one or both their parents were lycanthropes) are vulnerable to magical energy. Afflicteds (including being bitten, a family curse, or what have you) are susceptible to sonic attacks, or other sensory-based attacks (a bit like Daredevil).

What I'm stuck on is the classic full moon transformation. I've also thought that some lycanthropes could automatically transform at nightfall, like the Joe Fixit version of the Hulk. I'm just not sure which should get which. Should it be by power source, preferred form, or perhaps just an option the player could choose for their character?

Mmmm.... You could do turning into their preferred form at dusk on the three days of the full moon and back to human again in the morning, that shouldn't cause any problems.