Originally Posted by Varyon
The additional roll will often make the chance of success higher, because it puts the additional penalties on the second roll, not the first. Consider a character with skill 12 in a grappling skill, who hasn't trained up Grabbing Parry. With the two-roll version, to grab an arm that's punching at him, he needs to roll against 7 (his Parry is 9, -2 for Grabbing Parry) then 11 (skill 12, -1 to grapple an arm). His chance of pulling it off is (0.162*0.625)=10.125%. With the one-roll version, he needs a single success against 6 (Parry 9, -2 to Grabbing Parry, -1 for arm, as stated in the Technique), which is a 9.25% chance. If he had bought up the Technique to full, the two-roll version would be a roll against 9 then 11 for (0.375*0.625)=23.4%, while the one-roll version would be a single roll against 8, with a 25.92% chance of success. That's slightly higher, but if you work out probabilities for characters with skill above 12 (that is, the majority of characters who are likely to actually try Grabbing Parry), two-roll consistently gives a better result than one-roll. This also has the advantage of matching with the way Aggressive Parry and Jam work.
The roll for attempting to damage the target when using Aggressive Parry/Jam is unopposed, so if we have Grabbing Parry work like that, we don't need to worry about a QC. Indeed, as it stands, if we just add in this extra roll to Grabbing Parry, it behaves almost exactly as one would expect from an Aggressive Parry that replaces the strike with a grapple (the modifiers to hit are halved, as normal for hit locations when grappling, the only difference is that the damage penalty is in the form of using 0.5xST rather than taking a -3 to damage).
|