Well any race that is set up with the intention that nobody finishes, is going to have to be tough! There is little in the way of concrete information about the route which gets tweaked each year and with 3 finishers this year, heaven help next year's entry.
100miles is the stated length but most competitors believe it to be much more - nearer 125. As GPS is not allowed, nobody knows for sure. The climb is estimated to be somewhere in the region of 55,000 feet in total.
Yes there are some trails but a lot is off-piste in dense woodland covered with briars. A lot of runners come back from each loop ripped to shreds. The terrain is tough and combine that with the dense vegetation, navigation will be exceedingly difficult especially as at least half will be in the dark too. The weather is known for extremes of hot and cold, and frequently wet. One water station was frozen solid this year.
You can't use your own watch - you are given one but it will have come from a thrift shop and you'll be lucky if it works and of course, not knowing when the race will start is going to screw up your prep too.
There's a good documentary on it which I found on Amazon prime - other video streaming channels are available!