How come I can't get the potion achievement?

I keep getting "invalid combination", what does that mean? I tried it with my old pet, IoliteLazuli,which showed the same thing, and now the same thing with my Lilac Lain, formerly a Lilac Torrey.

Would anyone know why?

Which Potion are you using?

Not all pets can be every colour. You can check at Subeta HQ to confirm which pet can be which colours.

Other than that, I know there is a glitch with the common potion.

Common Potion does not work for the achievement

Everyone has pretty much answered your question. If it still doesn't work, fill out a ticket?

Vanish I would assume she was offering a suggestion. Unless she is completely off topic she is allowed to do that even if she doesn't know if it's the right answer.

I had that same problem when I tried to use the common potion. You may need to invest in a more expensive potion. Arid and Dawn are the two cheapest right at the moment.