Everything is designed to work seamlessly with each of the previous sets. So the Light and Dark and Core Set and From the Ashes all work together. In fact, there are a few fantastic creatures in the Core Set - but the game works fantastically alone or with all the cards (200+ of them).
Basically, you can mix and match all the cards to suit your personal play style. Or just merge them all together for a huge epic Emberthon.