Ranger ... Two- weapon fighting slayer ..... power crit + imp crit+ keen scimitar?

[Eldansyr77]

I am currently working on a 11th level Elven ranger 5 / bard 6. I wanted to make a pretty decent two- weapon fighter so if i get the twf and improved twf feats and ambidexterity that should nullify any penalties... now what if i took weapon focus (scimitar) and improved critical (scimitar) as well as power critical and a keen scimitar ... does all this stack in terms of critical roll chance? 20-6 for keen scimitar, -2 for improved crit (scimitar) and -4 for power crit = 10-20 crit range.... is this possible?

[Name1]

Keen and Improved Critical do not stack, they explicitly say so:
This effect doesn’t stack with any other effect that expands the threat range of a weapon.

Also, power critical doesn't increase the crit range, it gives you an additional +4 to confirm a crit.

What you could do, with you being a ranger and all, is sink 8 Levels into Disciple of Dispater and get yourself two Stump Knife Aptitude Weapons (one per hand) to be able to apply Lightning Mace to it.
The result would be a weapon that crits on a 15-20 for the first hit and a 9-20 every hit thereafter, giving you one extra strike at the same attack bonus everytime you threaten a crit, which might be what you are looking for.

[Khedrac]

Are you playing 3.0, 3.5 or Pathfinder?

I don't know for Pathfinder, but ambidexterity was a 3.0 feat that was merged into two-weapon fighting for 3.5. Thus you cannot take the feat in 3.5 as it does not actually exist.

Again, for the stacking of critical threat range increasers this is different between 3.0 and 3.5
In 3.0 things that increased the threat range usually stacked, e.g. improved critical and the keen enchantment.
In 3.5 they very specifically do not stack.
The interaction of them with other "on critical" effects (burst weapons, power critical etc.) is less clear. Most of the time they state that they do not stack with other "critical enhancing" effects, but it is not clear how to rule what happens when both are available.

My house rule clarification is that multiple dissimilar effects work in parallel:
E.g. Scimitar (normal): 18-20 (x2)
+1 keen, flaming burst scimitar with power critical:
15-17 (x2, no burst), 18-20 (x3, +1d10 fire damage)

I.e. none of the effects stack, but they all work on the base scimitar - but that is my house rule clarification.

Obligatory mention: The TWF OffHandbook (http://www.giantitp.com/forums/showthread.php?279079-3-5-The-TWF-OffHandbook).

Edit: Be wary of Disciple of Dispater - it is a 3.0 class therefore it is up to the DM to adjudicate on its conversion to 3.5. Yes, it explicitly states that its crit boost stacks, but pretty much all 3.0 crit boosts stacked so it would be a reasonable conversion to 3.5 to disallow stacking.

Edit 2: Corrected use of the wrong feat in my example.

[Name1]

Edit: Be wary of Disciple of Dispater - it is a 3.0 class therefore it is up to the DM to adjudicate on its conversion to 3.5. Yes, it explicitly states that its crit boost stacks, but pretty much all 3.0 crit boosts stacked so it would be a reasonable conversion to 3.5 to disallow stacking.

I've never understood why all of those conversion adjustments seem necessary. A lot of 3.0 classes seem to work fine in 3.5...
Anyway, Khedrac is 100% right on the Improved critical stack: Even if Discipline of Dispater says it stacks with Improved Critical, Improved Critical doesn't stack with the Iron Power ability, so it would be reasonable to assume it doesn't stack.