Settle down, this has nothing to do with Star Wars.
While having a discussion about class building and monster PCs, I had some inspiration for Fighter variants. As I wrote before, I have some problems with how to create variants of the Fighter class. Non-combat class variants seem like they should really be Support (Thief) variants, if they are non-magical. And there doesn't seem to be much to vary in the combat realm.
But in a discussion on an old post about monster PCs, Ynas Midgard wondered whether the class building rules I've written about elsewhere could be applied to monster PCs as well. Monsters, as I see them, are mostly either primarily Fighters or primarily Magic-Users, although there are a few with thieving abilities, and you could certainly conceive of ways to use the Turn Undead ability or a variant of it to handle monster abilities. (I'll probably return to the latter idea in some future posts...)
If you rule out monsters with magical powers and look at the purely mundane (or supermundane,) you'll find occasional abilities dependent on physical structure: enormous leaps, swallowing whole, that sort of thing. What I'm thinking is that these abilities are primarily based on physical force or might, which distinguishes them from abilities that are based on talent (the Thief/Support abilities.)
Of course, you need a particular kind of body to do many of these things, so they are only viable for monster PCs, not variant Fighter classes for humans. But if you think of the physical abilities of a human that rely on force, particularly those used in combat, you could allow some minor physical variation (massive, powerful arms good for grappling) in exchange for minor inconveniences in armor or weapon choice (custom armor required.) And major physical variation (physical mutation) in exchange for more major inconveniences.