See, the thing is, CMC doesn’t change based on what you’re paying (except in one case which I’ll get to in a moment). The CMC is whatever is printed in the top-right hand corner of the card, no matter what you actually paid. Terminus has a CMC of 6. Always. It doesn’t matter if you pay 4WW for it, or W, or WUBRG, or for free, or for 7 because of Thalia. So, Mental Misstep won’t ever stop a Terminus, a Banishing Stroke, or a Revenge of the Hunted, because they never have a CMC of 1.
Now, like I said earlier, there is ONE case where CMC changes. That’s with X spells. In almost every game zone, X is always zero. Now, on the stack, it’s whatever you chose for X. So, a Fireball in your hand, your deck, or your graveyard has a CMC of 1. The X is 0. But on the stack, the CMC changes. If you drop a Fireball for X=5, that Fireball on the stack has a CMC of 6. So, because of that, there is ONE miracle that could theoretically ever be Misstep-ed, and that’s Bonfire of the Damned… but you can only Misstep it if they cast it for X=0, which you’re unlikely to see in your lifetime.
Today’s Rules Tip written by
Trevor Nuñez, Level 1 judge from Roswell, NM
**Title and suggestion for this topic from reader Joshua Locke