How does the Monk's Crushing Blow feat work?

Question

The Stunning Fist feat says:

You must declare that you are using this feat before you make your attack roll (thus, a failed attack roll ruins the attempt). Stunning Fist forces a foe damaged by your unarmed attack to make a Fortitude saving throw (DC 10 + 1/2 your character level + your Wis modifier), in addition to dealing damage normally. A defender who fails this saving throw is stunned for 1 round (until just before your next turn). A stunned character drops everything held, can’t take actions, loses any Dexterity bonus to AC, and takes a –2 penalty to AC. You may attempt a stunning attack once per day for every four levels you have attained (but see Special), and no more than once per round. Constructs, oozes, plants, undead, incorporeal creatures, and creatures immune to critical hits cannot be stunned.

The Crushing Blow feat states:

You can make a Stunning Fist attempt as a full-round action. If successful, instead of stunning your target, you reduce the target’s AC by an amount equal to your Wisdom modifier for 1 minute. This penalty does not stack with other penalties applied due to Crushing Blow.

I'm not sure how this all works. Crushing Blow specifies Full-round action, so I thought that it was just the Fort Save for the enemy, and then you'd get the effect, or you wouldn't. Since there is no normal attack, that can't cause failure either, but you also can't deal any damage.

During play, I found out others didn't agree. Their interpretation was that I still had to make a normal attack, and then if hitting attempt the Crushing Blow - sort of like a different effect option for Stunning Fist that prevents Move Actions?

So how do I use this feat? By itself or as part of a Standard Attack hit?

Answer 1

Unfortunately, the eponymous 'others' are correct. I'll break it down:

First, you declare use of the ability and make an attack.

From Crushing Blow,

You can make a Stunning Fist attempt as a full-round action...

and Stunning Fist,

You must declare that you are using this feat before you make your attack roll (thus, a failed attack roll ruins the attempt). Stunning Fist forces a foe damaged by your unarmed attack...

Nothing about Crushing Blow says you do not make the attack or automatically hit. You are still using the same ability (Stunning Fist), just with a different outcome.

If you hit, deal damage and the target makes a Fortitude Save.

Stunning Fist/Crushing Blow trigger off of "damage [of] your unarmed attack". If you deal no damage (such as by missing or failing to overcome DR/Hardness), the target is unaffected. Upon successfully dealing damage,

...forces a foe damaged by your unarmed attack to make a Fortitude saving throw (DC 10 + 1/2 your character level + your Wis modifier), in addition to dealing damage normally.

If the target fails their Save, their AC is reduced for 1 minute.

Crushing Blow works exactly like Stunning Fist except with a different outcome.

instead of stunning your target, you reduce the target’s AC by an amount equal to your Wisdom modifier for 1 minute.

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Why is it not the other way?

If it were an automatic Fort Save, the wording on Crushing Blow would be different:

You can [expend] a [use of] Stunning Fist as a full-round action. [If a target threatened by your Unarmed Strike fails a Fortitude saving throw (DC 10 + 1/2 your character level + your Wis modifier)], instead of stunning your target, you reduce the target’s AC by an amount equal to your Wisdom modifier for 1 minute. This penalty does not stack with other penalties applied due to Crushing Blow.