Good reasons.

And they have a lovely afternoon hardly overshadowed at all by worries about irresponsible alien war crimes tribunals.

Meanwhile outside, he would like to walk on the water and starts singing the song for it. 

It works fine, of course. All of the other Elves stare.

He stops singing and plops in and requires rescue and - "sorry, are we not supposed to run on this lake?"

"No, my lord prince can run on any lakes he wants, just... how were you doing that?"

"You haven't invented the song?" he says, surprised. 

"You have a song that lets you walk on water?"

"Yeah, of course, how else do you cross rivers?"

"Sing it."

A short while later everyone gets a note - "soul Elves can sing magic songs, can teach us the magic songs, can in principle compose magic songs but none of them know how."

He doesn't get the note until a while later, but - "huh."

"Huh?"

"Soul Elves have magic music, discovered this when small me decided to go walk across the lake singing a waterwalking song and then asked confusedly how anyone else crossed bodies of water."

"...soul Elves. Walk on water. Okay. What else are we missing, I wonder."

"Yeah, exactly. We should - call a meeting or something, have everyone prepare a summary of all of the potentially relevant stuff in their worlds..."

"Sounds good to me."

So he sends out a message, and people gradually trickle into the main bar for snacks and magic system briefings.

"I don't actually know how to compose magic music, it takes Years to get the hang of and I thought we had all of forever. I could introduce you to some people, though -"

"Please."

"Effects tend to be localized and limited in duration - usually to the length of the song, or not much longer - but if you move something it'll stay moved - most of the ones we know now were developed beside Cuivienen - grace and balance, warmth, calming a crying child, waterwalking, silent movement..."

"How long does it take to write one if you know how?"

"Inside of a Year? Depending how complicated it is, of course, I suppose some people might spend five getting something really efficient and easy to sing before they shared it with everyone..."

"Do they work recorded or hasn't that been checked yet?"

"Recorded?"

...Cam holds up his computer and puts on a few seconds of music.

"Oooooh, clever! That has not been tried."

Cam starts a list of things to try. "How, uh, how does a song for silent movement... work."

"Only the singer can hear it."