In case you weren’t aware, it’s possible to cast the Claws with X equal to 0. Normally, it wouldn’t deal any damage when it resolves. However, if you control a creature with a power of 4 or greater when the Claws resolves, you’ll deal an extra two damage, turning your Claws for 0 into an effective Shock.
So let’s say I control a Shaman of the Great Hunt, and I really don’t like your face down creature. So I cast Crater’s Claws, targeting your face down creature, with X equal to 0 (I mean, why waste more mana than I have to?). But you’re very protective of your face down creature, and so you Murderous Cut my Shaman with the Claws still on the stack. What happens?
In this case, the Claws only checks to see if I control a creature with a power of 4 or greater at one time: when the Claws resolves. It doesn’t care about the power of my creatures at any other time. Since you removed by Shaman before the Claws goes to resolve, the Claws sees that I don’t control a creature with a power of 4 or greater, so I don’t get the bonus effect, and your face down creature isn’t dealt any damage.
And note this works both ways. If I have a Bloodfire Expert on the battlefield and I cast the Claws with X=0, the prowess trigger of the Expert resolves first (making the Expert into a 4/2), then the Claws resolves; and since I now have a creature with a power of 4 or greater, the Claws will get to deal an extra two damage.
And now that you’ve been educated about the proper interactions of Crater’s Claws, share this knowledge with your local FNM group and enjoy your weekend!
Today’s Rules Tip written by Nathan Long