The arms are VERY long, gives it a very ape-like look. Perfect for picking things up and throwing them, much more interesting than just 'yeah I can hold big guns lol'
For weapons, having the fist morph into a gun would be pretty awesome too, like astroboy.
The realistic, possible equivalent of this is have the fist as a weapon, and you change weapons to morph it. I'm sure there's a tricky way of animating it to transform, even if it transformed for each shot, then transformed back again (using the minigun code).

Nice work so far!

My initial plan was to make a rocket fist, but I don't know if I can add an attachable "fake fist" to the hand/arm that I can hide when the rocket fist gets shot off.

You mean like a pink sprite that covers the original fists?

Anyway, this thing is taking shape and I like it. Rocket punch is going to be FUN, and fits well into the Behemoth. Will it be a mass based-only weapon?

So are the hands just going to be weapons?
That would make sense, like when you switch weapons it's "attached" to your arm, but just held by an invisible hand.

thats due to the way 3d works, i expect.