Ok, simple issue here.
I take a squad of 3 Obliterators with the Mark of Tzeentch, this gives then a very handy 4++.
If I then park those Oblits on a Skyshield with its defenses up, which ALSO awards a 4++ save to the models using it, do I now have a 3++ save?
The issue only really arises because the Mark is on the Oblits, not the Skyshield. But the Skyshield gives the Unit a 4++ save and Tzeench boosts any invun save they get by one.
How do we think this works?
This sounds reasonable...
I mean Skyshield is worded this way, although you won't get any protection from barrages per se, but I think you're otherwise good to go.
I'd run it by your opponent first just before you deploy so there's no confusion later though.
Best,
-BT
Just from the top of my head, as no books to check on at hand, but is it not a cover save you get from a skyshield? So if the mark says invulnerable then people could argue it does not apply? As the two saves are different from each other are they not?
The Skyshield give you an invunerable save if the shields are up. If they are unfurled then I suspect you only get the area terrain cover save.