I imagine this MORE detailed than DFs system, and also considering these are Einherjar; The warriors of Odin (at least in this game) do not feel pain, they do not become sick, and fasting every night so starvation is a non issue.
Think more Toribash; physics based, limbs flying in all directions and completely free-form action movie-style flying awesomeness. Fire and cold should absolutely make it in.
Everything will be explained better by powergoals.
I don't think magic of that kind is any good idea, you are an Einherjar, a *warrior*, the player should NEVER become a mage-like character.
Of coarse there should be plenty of magic, but it's the magic of the gods, the magic the player might use is passive, for example we are quite safe to assume the weapons used by the chosen warriors of Odin is outside the ordinary.
In viking mythology even the gods rarely use direct spells, Tors lightning is a physical hammer, and animal form is archived by a magical, and much more serius, version of masquerade suites.
The most common obvious magic will probobly be the Valkyrie or a thing I'vr made up myself; wooden training giants; giant wooden golem-like training dummies made to mimic a real giant, for look think Transformers of wood that would become a classic longboat if needed traverse water (they don't transform, but they contain about the same parts as a ship and follow the same visual theme, of coarse as this is ASCII you won't see them).
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Some Powergoals:
POWERGOAL 003: JUST A FLESH WOUND: You are fighting inside a large windmill like structure, and you fall and get stuck in one of the giant wooden gearwheels, as you begin to be gridded a Valkyrie catch sight of you from outside and quickly dive in and pull you out, she then looks annoyed at the pool of gore that once was your lower body, knowing she will have a lot of work tonight.
POWERGOAL 004: STRIKE THE EARTH: You are fighting a wooden training giant (WTG for now, until we can get a proper Nordic name) measuring five men in hight. You swing at the giants leg but it glances away and the blow strike the earth! The giant points and laughs and rises a fist to deliver a crushing blow, but the laughter turns to horror when the giant notices that your axe struck flint and the sparks set its wooden leg ablaze! son the WTG is burning like a bonfire and runs screaming thought the Einherjar hoard, it runs down a cliff and you loose sight of it.
POWERGOAL 005: OUT OF THE MATRIX: You have somehow acquired two double axes. You run forward and strike two Einherjar simultaneously in the head! you use the inertia to propel yourself high into the air and as you land you spin around arms outstretched and decapitate of several Einherjar as you land, as you take ground you roll, striking the feet you from under some more Einherjar so your team mates can finish them of before jumping up and landing a kick in the belly of another one making him fall of a hight cliff, as you do this you whirl around and stand face to face whit on of your best friends. you both let out a roaring laugher simultaneously, your team won todays battle.
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I find I quite enjoy writing these, I have many more ideas, but they take a bit of time and I want some feedback, so this is enough for today.
I will try ti make one specifying a bit abut the feasting arc soon, but generally it involves a random song generator, lots of mead, and the battle logs of the other Einherjar that was also simulated but outside you view.
Sorry if I act like this was my game, you use so many of my ideas that I just assume you will use the rest to.