My questions: Does it stack? I don´t see anything that interferes with a good old YES^^

quite deadly. You just need a character capable of using them to their fullest. Which is tougher than it seems, depending on your take on the free spirit chargen rules that we're currently discussing in another thread.

The question is:
WHAT EXACTLY does qualify as a natural Weapon?
Bite? Everybody has teeth. Claws? Well, Fingernails at least.
Punch? Kick? Bare handed / bare feeted? Headbutt?
Trolls got Horns. And then there's Goring Horns.
And Surge Claws and the such . .

Having the Natural Weapon Power qualifies, and nothing else does.

Why wouldn't these stack? Energy Aura gives a +4 and an element, and works with any melee attack at all; while Natural Weapon gives (typically) a Lethal unarmed. (I'm assuming you meant Energy Aura, because I haven't heard of Elemental Aura, right?)

Elemental Aura is the equivalent spell. My druid uses it with water. makes cleaning up afterwards easier...

Thanks, Makki! I finally found it in Street Magic: [Element] Aura.

Starts to Get sick with physical adepts with killing hands and critical strike adding in a F5 flame or electrical aura adding to his damage gets sick.

Of course, you could just use a gun. Still, 'handy' if you need to can-open an armored car or disrupt a spirit.