God creatures?

So, in every realm, there’s a god. (Duh!) When reaching a certain rank with them, creature cores/gems are unlocked.
My question is, how are the creatures in comparison to what you normally find in the wild (realm)? Also, during encounters some creatures have the big red “X” (you can’t extract cores from.) Are they available for extraction at a later realm level, or unlocked through breeding? They seem pretty generic (opposed to something specialized).
Thanks in advance.

Most of the creatures that have a red X on them can be extracted from once they are bred with a breeding combination. Or, finishing a castle quest.

The cores that are bought at the god altars can’t be extracted from.

The pool of enemies increases as your realm depth increases