I am also glad to see lots of questions, thanks RSJ! I will have a Designers Notes article in the #0 issue of The Cauldron. At the same time I don't want you to think I am just going to leave you hanging and waiting. As long as your happy to re-read parts of this in The Cauldron, I am happy to do a bit of elaboration now.
Endurance is what sets the Heroes (and arch enemies) apart from the normal terrors or opponents. Its their ability to absorb (or through spell casting cause) extra damage without resorting to a Hit Points stat or other odd calculations. Fatigue in some systems mirrors this for Wizards, but if you are going to go that route, why not just make it an attribute that any Hero can benefit from!
Remember unlike d20 games, there are no levels and no increases in HP (or attributes as in TFT) you build it...and that's it for the life of your Hero. Yet as EN recharges quickly it aids Heroes in giving them additional spell casting power as well as letting the Heroes continue to adventure after a set back in battle.
Now how to equate (or balance) Heroes and Terrors in battle if the Terrors have no EN? Well if you are shooting to balance encounters, just compare ST value total of Heroes vs. the ST value total of the Terrors. The total for the terrors should be equal to or higher than the Heroes. I usually add 1 or two extra terrors. Now that's just a rule of thumb and it allows the Heroes to cut through larger numbers of enemies across a longer adventure.
And some news...
Issue #0 of The Cauldron will come out in December, I am hoping to include some unique spells from a contributor, a refereed adventure, and a sample solo programmed adventure playable with an included NPC. It will give the curious a taste for the system if you want to try it before you buy. Second it will be provide a good taste for what's to come overall as future issues will be for sale.
A dialog has started about a potential well known setting made for HOW. Hopefully the stars will align and some good news can be shared soon.
Lastly, if you are looking to kick off an adventure, I highly recommend checking out the adventures at Dark City Games. Each include battle map, counters, and is programmed so you can play it solo or in a group!
Looking forward to seeing a review!