12.02.02Whenever CARDNAME deals damage to a white or blue creature, double it.

change "whenever CARDNAME" to "if CARDNAME would"

because whenever means it's already happened- so it'd be too late to make the change of doubling the damage. you want a replacement effect not a triggered ability

"If ~ would deal damage to a white or blue creature, it deals double that damage instead," is, I believe, the right wording.

For some reason I want to propose amping this up to say "a white or blue permanent", so that it can double-hit planeswalkers too. But you certainly don't have to make that change.

Awesome, thanks for the suggestions. I definitely like the design flexibility of it possibly hitting a planeswalker also for double if if the wording sounds strange. I'll change it for now even if that ability is probably too powerful for this common of a card.

If CARDNAME deals damage to a white or blue permanent, double it.