Ruling Regigigas

[Celebi23]

I'm in a big rush and can't post scans this time, sorry. But I kinda need an answer before states tomorrow. Fortunately, the cards are commonly used. If I attack with Regigigas-EX's first attack after having played a PlusPower, but also have an Eviolite attached, and choose to do the extra 20, will I have the option not to inflict self-damage, or will it have to be inflicted?

I think this is slightly different than Bolt Strike + PlusPower because if the self-damage is zero, you don't add to the self-damage with PlusPower. If I have an Eviolite attached, I would think I could choose to use that effect before PlusPower, setting the self-damage to 0, making PlusPower self damage not activate.

 

[CarlosDuranJr]

The damage is calculated before eviolite comes into play. So, choosing to do 80+ 10, you'll still do 10 to yourself.
Like plus power double defender bolt strike does 10 to Zekrom

 

[DNA]

A rule of thumb:

First you apply everything that increases attack damage,
then you apply everything that decreases it.

This isn't true in 100% of cases (Machamp X's No Guard was one of those cases), but it's generally true.

Also, all the adding/subtracting is considered to happen "all at once" as far as the game goes. You don't stop midway if you find out the damage calculation equals zero; you finish all the steps.