Something bad would happen because they are different blood types they cant mix because I dont really know how to explain this but ill try. It has to do with our antigens and our blood cells have many antigens that our ignored by our immune system for some reason. If you get a different blood type your antigens will attack the other antigens because they dont match the ones that you have. So if you get hurt or something and end up in the hospital and your bleeding out and need a blood transfusion if the doctors were to give you a different blood type your blood would attack the different blood and you die
