Potions do not reproduce themselves without one of the ingredients being present in the other parent too...

So if you breed a Potion to a Pastel you will just make Mystics, Mystic Pastels, Mojos and Mojo Pastels...No Potions or Potion Pastels...

If you want to make Potion Combos you need to stock up on Mojave Combo females now...Raise them up a year and then get a Male Mystic Combo to breed to them when they are ready...This is that best/fastest way to make Potion Combos.