To begin with - I’ve completed all three faction missions to unlock final mission at Palace (New Jericho first, then Anu and Synderion), halted my virophage research (because it’s like some desperate “i hate everything and everyone” kind of scenario). I’ve read a lot of forum/reddit messages about this mission after my first try - how unbalanced it is and how it should be reworked, that’s not my problem. First of all I’ve read people use their priest level 6 ability with psychic immunity, but it literally does nothing for me (not just for units around the priest, but priest himself get MotV applied on him), was it patched at some point? And after I’ve finally finished the mission, I’ve placed the beacon, there was little animation of placing the beacon, mission end screen and after that… nothing. I got back to Geoscape, there was still Palace mission on the map and “The Plan” special mission from New Jericho, is that a bug?
Apparently, the devs never wanted the MotV to be a psychic attack. Early on, I believe that the priests did protect units. The devs saw this as a bug, since they don’t see MotV as a pyschic attack, and “fixed” it.
As to the bug with the final Palace mission, this was introduced with the Arkham patch/update. I have reported the same thing (via F12) following the Anu ending. Though some people can’t get F12 to work for them. Again a bug introduced with the latest update.
Yeah, Mark fo the void is entropy or pure damage, however, you want to call it. It is not supposed to be countered.
About the bug with the final mission not ending the game, we are aware of it and will fix it in a hotfix that will come soon. Sorry about that.
Ahhh, so currently its “neverending story” 
Yeah just found reply from… august this year, I understand mission and boss being difficult but with MotV there should be some counter-measures - and I thought priest ability was it. Otherwise it should be like… certain duration for MotV, or “it deals damage to units in a radius, not to the unit itself” so it makes you to position your squad accrodingly etc., well I guess people pointed that out previously already. Thankfully I did save the game just before finishing the boss and hopefully save files won’t get corrupted if it’ll be fixed 