What do you think would happen if the sirens discovered the portal to Equestria and used it? We’ve seen what they look like in non human form, and they’re definitely not ponies, yet they turned in to exactly the same things that Twi and Sunset did when they used the portal. Yet Spike, also a non pony creature (and may I please point out the fact that the sirens actually look a lot like dragons!) turned in to a dog.
So how does the portal work, and could the sirens just go back through it? If they did, would they turn back in to the dragony things minus dark powers, or would their lack of magic make them turn in to normal ponies or something?