Based on (Different Attribute)

Based on (Different Attribute) (B102) aka BODA is a multi-option enhancement category found on B102 meant to alter resistance rolls.
==Etymology==
It is intended to be renamed, substituting (Attribute) with the attribute. For example, the four primary attributes:
*Based on ST
*Based on DX
*Based on IQ
*Based on HT
Despite the name, it is also to shift resistance rolls FROM or TO the two secondary characteristics of IQ as well: Perception (Per) and Will.
Possession at +20% might for example, require a different mental (IQ/Per) or even a physical (DX/HT/ST) roll to resist, instead of the usual Will roll.
==Exploits==
Normally something like Selectivity can switch an enhancement off, which should be able to allow someone to toggle between the default attribute and the substituted one. This would be possible under the basic set rules.
GURPS Powers contradicted this spirit with the middle column of P100. The new option "an attack can have several instances of this enhancement" (subject to GM approval) described a different mechanical approach. It now has a much more punitive policy:
:Each attribute – including the one that normally resists the attack – costs +20%.
It is not specified when/how the user makes the choice of which attribute. The specifics of that might allow for different variations. Following subsections give some examples.
===Selectivity versus Doubled Enhancement===
Buying it twice for possession ("Requires Will or ST", for example) as contrast with buying it once (Requires ST) and having Selectivity +5% to be able to turn that off and revert it to the default of Will.
Selectivity is implied to be something decided upon before launching an attack. For example you decide if you have "increased range" enhanced prior to making your attack roll, because that's going to determine how far you can shoot.
Using a selectivity approach an attacker would be obligated to decide whether to use "enhanced possession" (ST resists, not Will) or "normal possession (Will resists) before making the IQ roll.
If this is allowed: the benefit (for higher investment) of buying it twice could be to NOT require this choice be made before the attack/IQ roll.
"Attacker's choice" could be made flexible. You might for example specify "the greater of the two" if you WANT your foe to successfully resist, or "the lesser of the two" if you do NOT want them to resist.
===Alternative Enhancements versus Doubled Enhancement===
Alternative Enhancements are similar to Selectivity in that they probably also must be specified before committing to an attack. You would have to know before attacking (possibly even before Aiming?) whether you're using "Accurate +4 +20%" or "Double Blunt Trauma +20%" from an option pool of +24%.
Like Alternative Attacks this is probably a free action to switch between.
Alternative: "requires ST roll or requires DX roll" for +24% would force Possession [124] to specify either ST or DX.
This actually makes it slightly cheaper to specify the original attribute (+4%) than taking Selectivity at +5%, but Selectivity has the benefit of turning off other kinds of enhancements too, so it's usually the better investment. It would merely save a point if you had no other enhancements you cared to disable.
===Selectivity as an Alternative Enhancement===
It might be fair to allow Selectivity AS the alternative enhancement (costing +1%) in this case: a placeholder basically allowing you to switch off other enhancements when not using the Different Attribute, which effectively allows you to terminate that one too.
*the downside compared to standalone Selectivity is you're not able to turn off other enhancements without turning off the alternative: it's mandatory
==Reversal==
Powers pg 100 expands this with the option of buying it more than once to allow the choice of what to target:
*The GM may permit this modifier on advantages that require the user to roll against his own DX, IQ, HT, Will, or Per, shifting the roll to another of these scores.
This notably omits shifting one's own ST rolls to other scores, or shifting other scores to ST rolls. Going to/from ST only remains an option for enemy resistance rolls, but not one's own checks.
This was subsequently (like Blood Agent, Reversed and Conjured) given a distinct name in a later "Power-Ups" book:
*Based on (Different Attribute), Own Roll
==See Also==
*Attribute Substitution
*Requires (Attribute) Roll
*Spirit Trap
*Target rolls against the better of HT or Will
Category:Enhancements