Well, it has been well documented that many NB skills are bugged, but maybe a bit more in depth description of what is happening in your case or possibly even evidence supporting your claim will help this thread.

I can confirm that practically every Nightblade melee class spell uses Weapon Crit (but is still increased in damage by Magicka and, I BELIEVE, Spell Damage). This also applies to the Siphoning tree Ultimate spell, despite it not really seeming like a weapon hit.

You can test this by using Shadowy Disguise from the Shadow tree and quickly looking at your character sheet. Only Weapon Crit is increased by that spell, not Spell Crit. So, if Shadowy Disguise makes an ability crit, that ability uses Weapon Crit.

Impale is an execute ability and receives bonuses under a certain health % (30% i believe) thus does not benefit from the ability to ever crit.

I noticed the same stuff. No criticals for impale. Possibly need to unlock all passive abilities...

it would make no sence they would proc of of physical crit as they are spells that cost mana, it would undermine their whole class system.

Shadowy disguise> impale

I did some testing just now.

With 33% base weapon critical + Weapon crit potion I have 69% Weapon Critical.
With Shadowy Disguise on top of that, I have 169% Weapon Critical.

Impale still consistently does not crit.

With 7% base Spell Crit + Spell Crit potion, I have 43% Spell Crit.

Impale still consistently does not crit.

With the Spell Crit potion, Swallow Soul does crit however.

I'm going to write in a /bug report that Impale does not crit.

It makes no sence that the ability's use weapon crit they use mana either add it to the tooltip's (counts as melee or counts as magica) it's all just utterly confusing while it doesn't has to be.

Don't get me wrong i'm ok with ability's being melee crit, but atleast let people know that these ability's use either one or the other. So people can spec appropriately without going trough all the tree's trying to find out what stacks with what.

On that note i also think they should either add ranged crit melee crit and magica crit or simply remove melee crit and change it to physical crit. It seems they are using alot of terms inconsistently in the game(talking khajit last racial as an example here adds melee crit but it actually adds physical crit as it also counts towards my bow crit rate).

Realky sad that the class that needs more fixing/balancing is forgotten ob the upcoming 1.1 patch... I really dont know why we are being left in the cold...

I was also a bit confused by the crit factors, but learned to see that like this:

They basically doesn’t talk about physical crit, magicka crit or stamina crit. In the character sheet is clearly defined as “spell crit” and “weapon crit”.

So if you hit the target with a weapon, no matter if ranged or melee and no matter what resource the attack consume, magicka or stamina, as soon the target is hit by a weapon, the weapon crit should rule. The confusing thing is, that we have many weapon attacks which use magicka as attack resource and many players see a magicka consuming attack as spell. But agree, Impale doesn’t crit and I’d never understood what Impale is classified, spell or weapon attack. The fact that weapon attacks uses magicka as attack resource is another matter of discussion.

Still nothing about impale being fixed :S it still doesn't crit with either spell or phys crit.