What happens when casting Shapechange and Polymorph together?

Question

If I cast shapechange and then polymorph what will happen? What about in reverse order?

Can you tell me any examples please?

I am a little bit confused, but I imagine that after I cast shapechange I will lose my Supernatural abilities (Su), my type will become the subtype and my template. Then, if I cast polymorph, I will retain the Extraordinary abilities (Ex) of my shapechanged form and my type of shapechanged form will become my subtype and gain the type of the new polymorphed form, is this correct?

Answer 1

There is no reason you should ever do this

Shapechange gives you the magical ability to change form as a free action every round for as long as it lasts. You can keep changing from one thing to the next on every round. Shapechange does everything polymorph does, and quite a lot more besides.

When you cast polymorph, you change once, overriding any other changes you have. This form would follow the rules of polymorph, e.g. no Supernatural abilities. If you have not yet used your shapechange-granted opportunity to change this round, you could immediately override the change from polymorph with another change from shapechange, as a free action. If you have already used your shapechange change this round, (which would have been overwritten by polymorph) you’d have to wait until next round. Either way, your shapechange change could even be used to change to the form you already have from polymorph, but now with the extra features that shapechange offers.

But since you could have just taken that form, with additional features, by using shapechange and therefore not wasting any actions or spell slots, there was no good reason to cast polymorph in the first place.