Ah, this guy is a little short tempered, and tends to blow (he's based
off a volcano). When Erderra is angry, *gulp*, he tends to lose the
plot, and is very, very impatient.
Ok, this makes a lot more sense then. You could perhaps reflect Erderra's volcanic origins in the description. The myth simply states that "a ball of rock appeared" and I naturally assumed that to be granite or something. If, for example, a flame had appeared and out of it the black rock that would become Erderra, then the intended origin would have been a lot clearer.
Also, don't forget that this is in another world, you just don't know why the do and don't need to support life.
Again, I naturally assumed that everything but the Monsterra would be similar (in some form) to our known world.
As I think about it, this is an important point to writing your creation myth:
The reader should probably already know what is being created. That is after all, the way actual creation myths come about. People observe their world and then begin to speculate - trying to deduce how everything came about. If the world you are creating is not our own, then it would probably help to first establish how exactly this world is different, and use your creation myth to specifically explain those differences. That way, when we read the creation myth, everytime that we would naturally have a reaction like: "the order of these events seems all wrong", we can immediately understand "and THAT's why THIS is different in his world".