It's like Haste I suppose. The move allowance is doubled, but the stats don't change. Like if every square on the battlefield costs 1 move point instead of the normal 2. No more attacks, no more spells however. And (like other Pangaea unholy spells) it affects all undeads I think, not only "moss" carrions (unfortunately Vine Men, Vine Ogres and Dark Vines are not affected since they are not undead, but that's illogical IMHO!).
Cheers