This shows how certain units can turn into a 0/100 (or whatever base hp) and unkillable. This has a little story of how it happens. But if you can't figure it out from watching the units how to do it, either look at the triggers or Instructions. I checked all over the utilities and I don't see this done, I think.
This Utility gives a (somewhat) tutorial on how to make units become invincible to enemy attack. However, there have been several articles and discussions about this little feature/bug, and this little trick of the map editor was already very widely known, so I'm not sure if the need for this Utility was very high.
The presentation was only averagely done, and the explanation on how to do the actual trick is written in horrible grammar. In addition, the author does not actually accurately describe how to best perform the trick, as his method only allows you to do this trick on Villagers, Monks, and Trebuchets.
The author gains some redemption due to the fact that there is a very small story in his scenario, but poor map quality and bad explanation of the trick combined with the fact that the trick is already well known cannot allow me to recommend this Utility.