Testers needed.

This works if the priest actually has four runes. If he only has three, you need to enter the following commands in the console first:

@heroes1 = GetPlayerHeroes(1)
@hero2 = heroes1[1]
@GiveArtefact (hero2, 86)
@runes=4 check_runes()

Added 2 minutes ago
By the way, I've already completed 60% of the fourth mission. Whew, I love these maps! I have a huge army (from four cities already) + an Archer set; I don't think anyone will be able to defeat me. The green player is generally passive, except for those in the cities on the northern island; I haven't seen any of his other heroes (+ the one that was at the beginning, a new one).
The green stacks are all inactive; the mage and ranger are still sitting in the forest, the yellow keymaster isn't giving the key, and the church in the north also doesn't want to be visited. I'm embarking on an eastward march across the bridge...

Added 49 minutes ago
So, all the sand stacks were needed – I had to collect them by teleporting the hero, otherwise, I was short by one kilogram (I was lucky that 1100 grams dropped from it).
It was a bit disappointing to run around the entire map, and to return to the very beginning for the ring of exile, but it's all okay, especially since I've invested in logistics.
As for suggestions, in the video with the yellow keymaster chasing the hero, the last line is impossible to read – there probably isn't a timer set, which is why the duration is zero. I don't think I noticed any other shortcomings.
Oh, and the Knight Benedict (who runs from the southeast corner) could be made twice as strong, because he's too weak, he couldn't even capture a city.