I don't see moltres spamming the hell of meteor storm then thorwing(Ha-haa! Got it?) a bunch of fireballs.
But as JJJ said, Nine tails is a already old Monster of Japanese culture, same thing as Kappa, or Tengu, or Miyabi Ninjyo. You can also see monsters of other cultures, I believe the whole moskovia is based on russian myths, while gryphons and medusas are greek myths. But RO got a lot of random monsters with no really explanations (Alicel/Aliot, Beelz, Vesper).
*cough* i wasn't the one that pointed that out x3
but ya thats true....
but i think the basis behind the alicel, aliot, and other kiel monsters is basically a story about robots gone bad (lol theres like a thousand movies about this)
and beelzebub.... its another name for the devil, the name was mostly used in Shakespearian time ... it pop's up in one of his plays too
so i wouldn't say there random myths Dx
i'd say every creature, and every monster, has an origin =P
like one of the new monsters in 13.1, its a unicorn =P one of the most popular myths =P
PS: anyone know what the beginner's fly wings and butterfly wings are going to do? im curious about this XD they seem cool <3