I've got a scene where a small group of ponies are trying to fight a changeling, and I need a set of exact words for when the changeling commands them to stop fighting.

The idea is that when the changeling gives them the command, the ponies, forced by the changeling's magic to obey the command, cannot move, thus leaving them as sitting ducks. But the command has to be worded so as to allow the following loophole: Lyra Heartstrings, the only unicorn in the group, realizes that the command doesn't prevent her from using her magic to force her limbs to move, in a manner similar to what Twilight did to Fluttershy when Flutters was being a fashion model in the episode Green Isn't Your Color.

Any thoughts on how to word this?

6237673 How about, "You shall not move a muscle?"

just my take on it but

"Sweet Celestia my nose itches I wonder how I could scratch it."After a few minutes of thinking I see a pebble that looks like it would get the job done so I try and lift it with my magic. Too my surprise it works my magic still works. After scratching my nose with the pebble. Which was awesome by the way.I then try and move my one of my legs with my magic. It works granted its clunky and will take some practice But works none the les

sorry if its not what you where looking for

6237673 Difficult. "Don't move a muscle" is the first response, but it would technically also block Lyra. You see, the muscles in a leg move even if it's telekinesis moving them rather than motor neurons. "Don't flex a muscle" would open the loophole, but normal people just don't talk that way- the changeling wouldn't casually say it that way.

The difficulty here is that there has to be some reason for the changeling to say something more elaborate than the simple and universal, "Stop." There's no loophole to "Stop" or "Do not move". Give the changeling some reason to make exceptions to those, or to use some other formula, and then you make room for the loophole you want, but unless you do I think Lyra and her friends might be stuck.

6237673
"Your muscles can't support your bodies!"

This is similar to one I read in Worm fanfiction, where a Master (an hypnotist) orders a group of criminals to not resist arrest, and while most of them then sit down and wait to be arrested, one remains mobile by reasoning that there is a difference between resisting arrest and fleeing.

6237673 "Neuro-muscular block!"

You can't move your muscles if you can't send the signals.

"Listen as I cast my hex:
Not a muscle you shall flex!"

"Flex" isn't quite the same as "move." "Flexing" refers to the movement of the muscles BY the muscles, not by some force external to themselves. Plus, moar magicks! And that's always fun, right?

(P.S. Anyone wanna commission me to do Zecora lines? I've got a rhyming dictionary...)

"Freeze all motor functions!"

No, seriously. It refers to the brain moving/"activating" the muscles, leaving the "brain does magic which moves your muscles" option open on a technicality. It also avoids the problem of "OK, but how do they breathe?" unlike with the muscle flexing versions.

For real though, why doesn't the changeling just tell them to stop breathing? Kill themselves? Kill each other? What stops it from going full Kilgrave and just going, "Go to that corner and stand there for ever!"?

6237673
Hmm.. a bit of a conundrum.
one could possibly use an obscure phrase with symbolic meaning, seeing as it's accompanied by a spell OR is the spell.
Something like "THOU STRINGS HAVE BEEN CUT!!" would work.
If we think of the ponies being puppets, then cutting their "strings" would halt all musculature movement. (Without ceasing vital organs of course.) And in context, Lyra could magically "re-string" herself if that makes any sense.
Hope this helps!

I think there's a bit of a problem in any suggestion we could come up with, as any command to allow such a loophole would be both more complex and less complete than a simple "don't move", which would make its use pretty contrived and kinda dumb.

However, you could fall back on simple logic: if the command "don't move" gets thrown out, then logically that would also means you stop breathing. Or even stop beating your heart, since moving is kinda what it does 24/7. Since those probably won't happen it would stand to reason the intent of the person issuing the command is the important factor, not the wording. And from there it's a short step to go from "what did they mean" to "what didn't they think to stop".

What about 'not another step'? It stops most short (especially if they're charging at him), and it's simple, likely the first thing that would come to mind.
And then Lyra isn't stepping. She's self-levitating and manipulating her limbs, not taking any steps.