I did the "beast" last year with a group. These "races" are a lot of fun and a good way to test yourself. Being "in shape" is a good idea, but I can tell you anyone can do one of these. I saw every shape and size during the race. My wife did the race with me and she hates running. We would just run a bit, then walk and run when again when we could. The obstacles are nothing to be scared of as they are a fun break between the running. Things like jumping into mud pits, jumping over wood walls, rope climbs, monkey bars on overhead cargo nets, spear throwing, dragging and carrying thing etc. If you cant do a obstacle, its not big deal they just have you do 30 burpees instead. I took it easy and hung with my wife for 3/4 of the race and I finished it in 3 hrs. She finished in 4 and there were some finishing in 6+ hrs. Anyone thinking about getting fit and trying different things, should do this. I would recommend a camelbak, lots of energy type snacks and SUNSCREEN!
Thanks for the report! sounds like a great experience.