Is it safe to mix potassium alum powder with magnesium oil (made from water and magnesium flakes)? Will mixing these two together cause a reaction of any sort? If so, is it safe and is there an order in which one should be added to the other?
If you are not sure and you have to do the reaction, try it with small sample of $\ce{Mg}$ such as one flake. $\ce{Mg}$ flakes should react in water and will react with potassium alum.