Sera said this in her latest interview in the official Supernatural link ;) Issue #22

Hm, I always thought it was neat that the creeps in Supernatural all had their basis in mythology and folklore as I'm really into that sort of stuff. Principally, I don't mind that the writers will create their own monsters now. It'll be interesting to see what they come up with, but I do hope that'll be an exception and won't become the new rule.

Although I love the traditional, mythology/folklore based monsters I'm also excited to see what the writers can come up with. I love what they did with the angels and I think it would be cool to introduce a whole other strata of monsters that the boys have to figure out how to kill on their own [meaning trial and error- not research].

I think that's great, I can't wait to see what they come up with!But I do love the creatures, the folklore and mythology that surrounds them that's already been established:)

I guess the worm-like creature that will appear in the next episode could be one of those made-up monsters.

I really liked the urban legend/mythology/folklore based monsters. I would love to keep the monsters Google-able, but I'll have to wait and see. Don't ditch until you try it!