>>42311372 (OP)Most likely you could not even exist in their universe. Different laws of physics would cause your body to disintegrate or even violently explode.
Now, if their universe did have compatible physics. And a breathable atmosphere. You would still have an issue with food. Given how they are of a completely separate tree of life to you, its unlikely their food will be edible. And even if its partially edible, like having compatible sugars, they won't have the right proteins so you would starve to death.
Now there are other potential issues. Human biology is rather sensitive. So even if the laws of physics match, exposure to magic could seriously fuck you up. Having no magic of your own you would have no defense against foreign magics. And if a unicorn directly used magic on you, you would likely be utterly screwed. Consider how badly a simple telekinesis spell would mess you up if it applied lifting force to your internal organs.
In regards to incompatibilities with magic. I came up with an interesting idea once. The equestrian sun is not a physical object and it does not produce visible photons. Its a source of magic, and ponies eyes don't see light, but rather magic. When the human gets to equestria its pitch black. All he sees when he looks to the sky is stars. Equestria is a rouge planet maintained with magic. The human after stumbling around in the dark eventually finds a small source of light, that being a lit candle. Later on, the human would have a reputation of always walking around with a burning torch, since its the only way he can see anything. (note candles emit magic as well as visible light, due to the combustion of organic material that is infused with magic). Also, there is a type of fire that is very dangerous to ponies, invisible fire caused by the burning of magically devoid materials)