It's a poor choice of wording there. Agreed.
But why would you use "one" if it means "any" or "all" or "each"?
It is not if one reads more than one sentence. But try it:
Let's try it:
If you’re able to make multiple attacks with the Attack action, this attack replaces any of them.
That would refer to the order of attacks - so it replaces any of the attacks (1st, 2nd or 3rd etc.) rather than a specific one. This part of the rules refers to action cost of using the push (attack action = push, if multiattack: 1multiattack = push) so there is no need for specifying "any". It specifies "one" as opposed to "attack action" that would include all of them.
If you’re able to make multiple attacks with the Attack action, this attack replaces all of them.
That means that push replaces each attack in the multiattack. Uneeded addition as "attack action" already consumed whole action. The meaning of this sentence would be the same as the first sentece in the rules (attack action = push)
If you’re able to make multiple attacks with the Attack action, this attack replaces each of them.
Again weird, and not sure what that would mean. Possible same as "all" but it just feels weird to read.
That brings us to how it is written:
If you’re able to make multiple attacks with the Attack action, this attack replaces one of them.
One attack of the multiattack = push
I am shocked there is even discussion here. I would hate to play any boardgame with you guys. There is not a single thing said about limiting use of push - if that was the case it would be stated, possibly not in the same paragrath as it wouldn't refer to action cost of using the skill. Even if wording can seem vague without context rules will always communicate one thing. So in the context of reading:
Using the Attack action, you can make a special melee attack to shove a creature, either to knock it prone or push it away from you. If you’re able to make multiple attacks with the Attack action, this attack replaces one of them.
Does the second sentence mean:
a) if you have multiattack, push will consume only of of the attacks rather than whole action
b) Regardless of multiattack you can perform one push only
It can't mean both - I have never encountered a situation when one short sentence would be used to communicate two different rules. Even if you pick "b" than we do lack a third sentence that would establish that we can use push as a part of attack action, because you just said that this sentence doesn't do that.
If intention would be to limit use of push per attack action it would go as follow:
Using the Attack action, you can make a special melee attack to shove a creature, either to knock it prone or push it away from you. If you’re able to make multiple attacks with the Attack action, this attack replaces one of them. You can perform one push only per Attack Action
- first paragraph of each skill
refers to action cost of using it. Push and grapple communicate only that in case of multiattack pushing/grappling consumes precisely one attack of the multiattack. There is nothing said about limitation of that exchange, so by the rules such limitation doesn't exist.
