But as far as Mudder is concerned, I'm not worried about the running. There are so many obstacles that you're never running more than a mile or so at a time.
It's the cold, muscle fatigue, and cold that are on my mind.
This was what I thought going in as well, but is probably the wrong approach. It is a lot of running and a lot of really tough running. I would suggest finding yourself a hilly trail and working up so you can run about 10 miles comfortably. Once you get out there and your shoes are soaked, you're weighed down by mud and you're trying to run uphill and side hill on uneven ground, you'll understand why the running preparation was so necessary.