Oscar carramiñana said:if you are inmune to critical you are inmune to vorpal effect.
The fortification has a % of ignore a critical - vorpal effect
DragonShadow said:A vorpal weapon would have to get through the fortification to actually be able to have the head popping effect. Meaning that, upon successful negation of the critical hit (depending on the type of fortification) you negate the vorpal effect as well.
UltimaGabe said:Even if a creature is immune to critical hits and sneak attacks, its head is still severed by a Vorpal sword- the only difference is that most things immune to critical hits can survive without a head.
Hypersmurf said:But the point is that Fortification doesn't, as written, make you immune to criticals... it makes the critical never happen at all. And if the critical never happens, Vorpal doesn't trigger.
-Hyp.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.