Crit Abilities Tied to 20s?

[Tevesh Szat]

In my playgroup (mostly, I believe, due to a degenerate halfling I had previously run), it has been enforced that any ability that triggers when you score a critical hit (such as the vorpal or tyrannical (runeforged) weapon qualities) cannot JUST be a crit, but MUST be a natural 20. I was just curious if this was my GM's houserule to keep a character from wrecking a storyline, or if there was actual precedent to it? Either way, I support his decision (a rogue with an inherent magical boon to add a +2 vorpal weapon quality to any bladed weapon wielded carrying a keen kukri means decapitating on a roll total of 12, and I can definitely see hesitation in letting that carry on), but I was honestly just curious.

[The Archive]

Vorpal requires a 20 to trigger no matter what the crit range of the weapon.

[Bart Vervaet]

How can you crit on a roll of 12??
Keen kukri gets a threat range of 15+, and doesn't stack with any other way to improve crit range.
Vorpal only triggers on a natural 20, but other crit dependent feats/abilities should trigger whenever you score a crit.

[Zaister]

Bart Vervaet wrote:

How can you crit on a roll of 12??

Probably ignorance of that fact that effects that extend the critical threat range of weapons do not stack.

[Blackstorm]

Just to note: vorpal ability is triggered only on a 20 because it's clearly stated on his description. The runeforged weapon need just to score a crit, as all the other weapon enhanchement that triggers on crits: if not otherwise specified (see vorpal) they trigger on a confirmed crit, wheter or not you roll a 20.

[Movin]

So I'm assuming that your group might have a few hold overs that played in 2.0 or 3.0 where the effects you have described worked as stated.
(crit stacking and vorpal weapons decapitating on a roll of 3 if you happened to worship the right demon lords.)
vorpal weapons were stupidly lethal and got hit quite heavily with the nerf bat. Entirely deserved in that point, though every setting has its problem children.

Unless explicitly stated in the description block (like vorpal) abilities that trigger on crits work on all instances of crits.
So your GM is running correctly on vorpal. Makes elemental burst qualites like flaming burst useless with the exception of stuff like heavy picks or scythes though. A critical from one of those would kill without the extra help anyway so the ability does decline in value with that house rule for weapons on average.

PRD Vorpal wrote:

Vorpal: This potent and feared ability allows the weapon to sever the heads of those it strikes. Upon a roll of natural 20 (followed by a successful roll to confirm the critical hit), the weapon severs the opponent's head (if it has one) from its body. Some creatures, such as many aberrations and all oozes, have no heads. Others, such as golems and undead creatures other than vampires, are not affected by the loss of their heads. Most other creatures, however, die when their heads are cut off. A vorpal weapon must be a slashing melee weapon. If you roll this property randomly for an inappropriate weapon, reroll.

Strong necromancy and transmutation; CL 18th; Craft Magic Arms and Armor, circle of death, keen edge; Price +5 bonus.

[Claxon]

As stated, Vorpal only works on a natural 20. Not a crit, but a natural 20 specifically (followed by a confirmed critical hit).

Also, as pointed out, your kukri should only have a crit range of 15-20. There are currently absolutely no options that increase crit range that stack. Paizo did this on purpose, so your crit range of 12-20 is simply wrong.

Other abilities that trigger on a critical hit should funciton normally* assuming the critical is confirmed. Remember rolling in the critical threat range doesn't make it a critical. You still have to roll well enough to confirm it, and only a nat 20 is an auto hit. So rolling a 15 with your keen kurki doesn't do didly squat if the opponents AC is 30 and your total attack is roll is 29 despite the fact that it was a critical threat.

*Provided that don't have some language similar to Vorpal which limits how they funciton.

[Zahir ibn Mahmoud ibn Jothan]

All of the various Critical Hit line of Feats require only a crit, and not a natural 20.