brehobit said:
I'll disagree with everyone. A weapon that allows sneak attack damage against undead should be a +1 modifier. And a weak +1 modifier at that. Bane against undead is generally better than this. With bane you
A) Always get to use it (even not flanking etc.)
B) Get a +2 attack bonus
C) Always get 2d6+2 extra damage.
In order to have grave strike be better than bane _assuming_ you were flanking, you'd really be looking at needing to have +4d6 damage from the sneak attack.
Except that we are not talking about weapon special abilities here. A continuous item would stack with a Bane weapon, or any other type of magical weapon for that matter.
So at 20th level, a Rogue could have a +5 Holy Undead Bane Flaming weapon which does with Strength modifiers 65+ points of damage per successful Sneak Attack against most Undead.
And, your A) above is not really that limiting. Most Rogues eventually acquire abilities such as Rings of Invisibility or Hide in Plain Sight or other ways to increase how often they either flank and/or deny Dex bonus.
The problem with the "since Bane weapons do a lot of damage, it is ok for Grave Strike to do even more damage" philosophy is the same problem that Bane weapons have in general.
A Flaming Sword does +1D6 against most opponents. On average, an extra 3.5 points of damage per successful attack.
A Holy Sword does +2D6 against evil opponents or an extra 7 points. 7 points does not sound like a real lot, but when you consider that a +2 Flaming Longsword averages 10 + Str damage on a successful hit and the same cost +1 Holy Longsword averages 12.5 + Str damage, it can be seen that the swords are not totally equal, but they are close and the Flaming Sword makes up for the slight difference by affecting slightly more opponents.
But, this philosophy tend to fall apart when you start restricting the number of opponents and really boosting the power of the item accordingly like with a Bane weapon. The same cost +2 Bane Longsword averages 15.5 + Str damage and it hits more often.
Say that a given Fighter with a 16 Strength has a 50% chance to hit with no magic bonuses. So, these three weapons average per swing, average damage per successful attack, and max damage per successful attack are:
+2 Flaming Longsword .6 * 9.5 * 1.1 (criticals) + .6 * 3.5 = 8.37, 13.95, 32
+1 Holy Longsword (evil) .55 * 8.5 * 1.1 (criticals) + .55 * 7 = 8.9925, 16.35, 34
+2 Bane Longsword (undead) .7 * 11.5 * 1.1 (criticals) + .7 * 7 = 13.755, 19.65, 42
+2 Flaming Longsword (resistant to flame) .6 * 9.5 * 1.1 (criticals) = 6.27, 10.45, 26
+1 Holy Longsword (non-evil) .55 * 8.5 * 1.1 (criticals) = 5.1425, 9.35, 22
+2 Bane Longsword (non-undead) .6 * 9.5 * 1.1 (criticals) = 6.27, 10.45, 26
The Flaming and Holy Longswords are fairly similar in damage, but the Bane weapon just walks away from the other two when it attacks it's special foe. It would be worse to add Sneak Attack damage on top of this type of thing, regardless of the item only adding it for undead creatures.
It is the stacking combined with a max of 10D6 extra damage (something that no weapon does, they max out at 6D6+2 and that is if you have something like a Bane Holy Axiomatic weapon) that makes a Grave Strike continuous item so potent.