Allfather Wargaming

When using the vapours of valtor tactics card, you place three obscuring mist tokens on a character and randomly pick one during an attack to see if the effect triggers or not. Is this chosen token discarded, meaning that there is 2 tokens left if a second attack is sent in? Or after it is drawn, the three tokens are re muddled and there are three for any concurrent attacks? Presumably too, if the token is drawn with the figure, the effect of the tactics card ends too?

So if I have Dr Strange in cover and he is attacked and I roll no blocks but then use the cover rule to change one blank to a block, does this trigger the shield of the seraphim rule and gain a power?