Your right about the X gun thing, thus explaining why it didn't kill the Tokyo team instantly.
Nurari doesn't seem to be capable of multi-tasking with abilities otherwise he would use the X-rifle theory of invisible blasts, the laser eyes, and become super strong all at once (before Oka, no sign of super strength was seen in my opinion because all he did was grab people or not touch the Gantzers but making them explode). Why is it that none of the Gantzers has tried using the X-Ray on the guns except for the one who confirmed he was the 100-pointer? maybe one of the other forms as a weakness in it? don't know yet though, hopefully something comes up in the sniping chapter.
A thought on his ever changeing abilties, the fleshless form or aka Skeletor form is known to move at superhuman speeds that out matches the Gantzers, possible ability to use explosions (leaning back to the X-Rifle/H-Gun theories) which is probably why the buildings exploded before Nurari returned, and breathing...was there any sign of Nurari breathing before since hes able to bend his shape and form at will? the only thing i found on him about breathing is when he laughs but that doesn't mean much. (yes i just disproved his inability to multi-task but since its only a theroy, the one above could be right). i believe you can see a heart to when hes skeletor on page 15-16 but its pretty useless since he might have the same organs as humans in all forms :\