So, Changelings are arguably the dumbest antagonist on the station currently IMO for multiple reasons. The chief among these, again IMO, is that almost if not all of the ling's abilities revolve around combat. There is nothing that these abilities do that can lead to some sort of RP that doesn't involve shooting. Armblade tends to give sec trigger fingers, Abomination gets shot almost immediately, and the stings are never really noticed by more than one person depending on the sting. My suggestion to fix this is in the title, Body Horror!
Now, what the hell do I meant by that? Body Horror is when a creature does something incredibly grotesque, like splitting their face in half, to scare those around it. In-game I imagine the changeling having this ability to do the same thing. Though this ability would not have any practical uses other than that, which I feel would encourage more RP that doesn't involve a robustofest. Now sure, you could simply /me these things, but that kinda depends on other people to notice and use thier imagination, and having it actually happen in game would make it more reactable then looking at some blank sprite face that is supposedly bleeding from every orifice according to chat. It would be something simple like blood showing up on the sprites face with red text describing what is happening. At the very least, this gives changelings a few glory moments before being gunned down, and at best can drive a new range of RP, including autopsies and the like, as I am sure science is curious as to what kind of creature splits its head in half on command. Though autopsies like that do happen, it is pretty damn rare. Imagine catching someone's doppelganger in a corner as sec, or seeing both of them in a hallway in medbay with everyone watching, and then seeing one of them have their eyeballs leave their head on tendrils, it would shock anyone in the room and most likely have everyone involved screaming for their lives over general.
I feel this is a necessary addition as, again, the Ling has basically nothing like this and has mostly combat abilities that are very hard to have any real RP with without either getting shot or people immediately running away due to knowing what that armblade is and what you plan on doing with it OOCly. At the least most people would read the red text and say something before booking it down the hallway. This is my first suggestion so if it seems lackluster that's why btw.