Case in point: the rogue's talents powerful sneak and deadly sneak from the APG:
Quote:
Powerful Sneak** (Ex): Whenever a rogue with this talent takes a full attack action, she can elect to take a –2 penalty on all attack rolls until the start of her next turn. If an attack during this time is a sneak attack, she treats all 1s on the sneak attack damage dice as 2s.
Deadly Sneak** (Ex): Whenever a rogue with this talent uses the powerful sneak rogue talent, she treats all 1s and 2s on the sneak attack damage dice as 3s. A rogue must have the powerful sneak rogue talent before choosing this talent.
A very simple calculation shows that Powerful sneak automatically reduce the DPR, except corner case (the rogue only hit on a 20 or only miss on a 1); Deadly sneak automatically reduce the DPR if the non-sneak damage of the rogue are at least one seventh his sneak damage, which means that if the non-sneak damages are at least 1d6+2, it can't increase the DPR (but it can increase the DPR of a 19-th level rogue using a silver non-magical dagger and who hit on 4 or more).
I already know why those talents are for: it's for roleplay reason, I guess. (Or at least, I guess that if I ask, SKR will answer that it's for roleplay).
Therefore my question is: what does those powers add to the roleplay of a character? How is the character with powerful sneak more roleplay than the one without?
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Annexe: details of the calculus.
Let's note P the probability of landing a blow, D_0 the damages without sneak attack, and S_0 the sneak damage without special talent. The DPR (without powerful/deadly sneak) is:
DPR(no talent) = P(D_0+S_0)
Let's note S_1 the sneak damage with Powerful sneak, and S_2 the sneak damage with deadly sneak, and N the number of sneak dice. We have:
S_0 = 1/6*(1+2+3+4+5+6)*N = 7/2*N
S_1 = 1/6*(2+2+3+4+5+6)*N = 11/3*N = 22/21*S_0
S_2 = 1/6*(3+3+3+4+5+6)*N = 4*N = 8/7*S_0
Therefore, if we assume no corner-case:
DPR(powerful sneak) = (P-0.1)*(D_0+22/21*S_0)
DPR(deadly sneak) = (P-0.1)*(D_0+8/7*S_0)
DPR(powerful sneak) > DPR(no talent) is equivalent to:
(P-0.1)*(D_0+22/21*S_0) > P(D_0+S_0)
P(D_0+S_0) + P*1/21*S_0 -0.1*(D_0+22/21*S_0) > P(D_0+S_0)
P*1/21*S_0 > 0.1*(D_0+22/21*S_0)
P > 2.1*D_0/S_0 + 2.2
But 2.1*D_0/S_0 + 2.2 > 2.2 and P can't be greater than 1, therefore, there is no solution: the DPR with powerful sneak can't be superior than the DPR without talent, except corner case.
For deadly sneak: DPR(deadly sneak) > DPR(no talent) is equivalent to:
(P-0.1)*(D_0+8/7*S_0) > P(D_0+S_0)
P(D_0+S_0) + P*1/7*S_0 -0.1*(D_0+8/7*S_0) > P(D_0+S_0)
P*1/7*S_0 > 0.1*(D_0+8/7*S_0)
P > 0.7*D_0/S_0 + 0.8
If 0.7*D_0/S_0 >= 0.1, then we need P to be greater than 0.95: we are in a corner-case, which is false by hypothesis. For the inequation to have solution, we need D_0 < 1/7*S_0 (and P>0.8: it doesn't have solution if the rogue doesn't hit on a 4).