At Pro Tour Origins, I was asked the following rules question:
Alice controls a Ghostfire Blade enchanted with Ensoul Artifact. Nadia casts Dromoka’s Command, forcing Alice to sacrifice an enchantment and, for lack of a better mode, choosing to put a +1/+1 counter on the Ghostfire Blade. (No – you can’t legally choose the first mode if you don’t have a spell on the stack it can target. No – you can’t make the Command target itself.)
The question is: will the Ghostfire Blade get a +1/+1 counter?
I ruled that YES – it does get a counter.
“But you sacrifice the enchantment first.”
While it’s true that you follow the instructions on the card in the order written, and therefore sacrifice the enchantment before putting a +1/+1 counter on the blade, putting a +1/+1 counter on a non-creature permanent is something we can do, and when resolving a spell or ability we do as much as we can.
“But it’s an illegal target!”
Kind of. The most important part of this interaction is WHEN we check for target legality. We make sure targets are legal when placing the spell/ability on the stack, and again just before we start to follow the instructions on the card. This is a case where the legality of the target changes DURING the resolution of the spell or ability – which is after we care about such things.
“But what about the line in 608.2b that says ‘Illegal targets, if any, won’t be affected by parts of a resolving spell’s effect for which they’re illegal.’ ??”
Great question! This line is specifically referring to objects that we’ve deemed illegal targets by this point. From here on, we’ve essentially locked in which targets are legal and which targets are not.
So, we end up with a Ghostfire Blade with a +1/+1 counter. (Remember that this won’t give an equipped creature +3/+3, but it itself will be larger if it gets re-animated at some point in the future.)
Finally, an exercise for the reader:
Alicia controls a Leonin Shikari and some Lightning Greaves (which are NOT equipped to anything). Natasha casts Orim’s Thunder with kicker, targeting the Shikari and the Greaves. In response, Alicia equips the Greaves to Leonin Shikari. What will happen when the Orim’s Thunder goes to resolve?