I’m a member of a couple of writing groups on Facebook and lurk a few on Reddit now and again. One thing I’ve seen over and over is that people seem to think they need permission to write things into their stories.
“Is this allowed in Science Fiction?”
“Can I do this thing in a Fantasy setting?”
Isn’t the point of creating your own universe is to create your own rules? Only once or twice have I seen anything in these questions that might not be a good idea. Most of the time these are things that with a good reason and explanation is perfectly possible if they want it to be. Plausibility is really the only limitation in fantasy and scifi, so long as you can make it sound like it could be happen go do your thing and write that into your story. You can have an island floating in the sky if you explain that it’s bedrock is laced with a magical material that defies the laws of physics. If you just say ‘because it does’ it is less plausible, but you don’t necessarily have to explain it although it is a good idea to do so.
The only people you are accountable to for what you can and cannot do in your own created world is yourself and your readers, if you see a reason for why something works and you can explain it in a way that your readers understand it and find it believable you are in the clear! Stop asking permission to write your story. The only thing you should go to your writing group for is “I’m doing this thing, help me make it work!”