does anyone know for sure? f.ex. I have rogue 1 and blackguard 4, they both have 1d6 sneak attack, so will I have 2d6 or still 1d6?

I've read somewhere that assasin's death attack stacks with sneak but in this case we have same name so maybe they don't.

i have taken level 3 blackguard for aura and CHA bonus to saves and thinking if it's worth taking 4th for better sneak .. because there is nothing else in it.

They stack, according to a Bioware moderator and the NWN wiki :

http://nwn.bioware.com/forums/viewtopic.html?topic=571441&forum=42

http://nwn.bioware.com/forums/viewtopic.html?forum=58&topic=449597

http://nwn.wikia.com/wiki/Sneak_attack

Yes they drefinitly stack. :)

(Only assassin has any issue with stacking of SA and this issue is the feat improved sneak attack won't stack with assassin's death attack unless you have at least 1 SA from rogue or Blackguard.)

Also, there may be another reason why you should take the 4th BG lvl. Base Attack Bonus (BAB) and number of Attacks Per Round (APR).

Your BAB is set by lvl20. After this it increases 1/2 lvls for everyone. The magic number for APR is BAB16 or higher. This gives you 4 unhasted APR (16/11/6/1). A pure rogue20 will have BAB 15 and so only 3 APR, so a popular decision for all 3/4BAB classes (rogue assassin bard monk druid etc (but not cleric for special reasons) is to take 4 levels of a 1/1BAB class (ftr, barb, ranger , BG, pal. CoT etc etc) to get the BAB to 16 and so get an extra attack.

If you are playing the OC this is probably not very relevant to you. If you are playing SoU and HoTU or community modules that go into epic levels it is. Whatever you do...

Have fun :)

What's so special in this regard about the Cleric, Shia? I routinely multiclass as a Cleric/Blackguard and I'm somewhat curious.

Divine Power spell, I think. Basically bumps up your base attack bonus to that of a same level fighter. There's definitely nothing wrong with the cleric/BG combo, though. Lots of synergy there.

Quotes from the wiki: http://nwn.wikia.com/wiki/Divine_power

Ah, thank You - that makes perfect sense. Still, I dislike spending 5 minutes buffing myself before a fight and as You already pointed out the Blackguard is quite a fine option for evil Clerics (as is the Champion of Torm for doo gooders).

Yip, Nomad got it. If you get BAB16 by lvl20 you already have 4 attacks, with the 4th at -15AB. If you design to have BAB15 at lvl20 then you only have 3 attacks and the 4th one provided by the spell is at full AB.

Blackguard could do with some more love imho, a spellbook for a start like paladin. But no use complaining *grin8 .... btw Blackguard bull strength spell stacks with cleric spell of the same name if you didn;t know.

Have fun :)

The lack of a paladinesque spellbook aside, I have but one complaint about the Blackguard - those five ranks in Hide make very little sense to me. Sure, there is some synergy with the Blackguards' Sneak Attack , but that's what their summons are for - to land a few "shneakey" hits in tandem. Besides - free proficiency in Medium/Heavy armor doesn't indicate a cloak and dagger style class and there always is the Assassin/Shadowdancer option for those who enjoy midnight knife-skulking.

Yip, couldn't agree more. Hide is not even a class skill for Blackguard! Makes no sense at all!

Have fun :)