As title. What is the general opinion of SCP's being created from already existing creatures of myth or legend (Ex, vampires, werewolves)? Is it something we should discourage or allow to pass?

No one should "discourage" or "allow" anything in terms of ideas. If you can execute a vampire or a werewolf, there's nothing stopping you.
The thing is, it's extremely difficult to execute those things properly because everyone's seen them a thousand times before. And most of the time SCPs based on existing mythological/popular/horror movie figures crash and burn. But that shouldn't stop people from trying if they think they can make it work.

As Kalinin said, it's very difficult to come up with an interesting take on most popular culture monster mythos, since by their very status as pop culture monsters, they've been presented, interpreted, reinterpreted, deconstructed, reconstructed, analyzed, mythologized, demystified, glorified, normalized, accentuated, tweaked, overpowered, underpowered and turned sparklypoo. Essentially, they've already been worked on in almost every conceivable way by such a large number of people that it's extremely difficult to come up with a unique and interesting take on it. The few we do have actually tend to focus on something other than the monster itself.
For instance: SCP-008 is the zombie virus. We all know it's the zombie virus. All it does is make zombies. But the focus is NOT on the zombies, but rather the virus and how pathological and contagious it is. Plus the lovely little worry about what happened/is happening to those samples that were held by the USSR before the Soviet breakup… There are a couple of others; I'm pretty sure I've seen a vampire one and a werewolf one, plus we have a couple of different angels and demons. Frankly, if you're going to make a SCP based on an existing mythological/religious idea, it's best to do so using an obscure creature/idea.
Giving bearhugs to the unsuspecting since 1872.

I say the more obscure, the better- I mean, take Babylon's demonology for example. That is some whack shizz, believe me, and I'm sure there's more than one SCP in it.

If you think you can pull it off, sandbox it and run it past the chat, but it's going to be a lot harder than most other kinds of SCPs.
Piffy is an SCP Foundation Moderator, Lv. 9001 Squishy Wizard, and Knight of the Red Pen.
I consider obscure mythology to be more problematic than the mainstream, seen-it-a-million-times things like vampires and werewolves. If someone puts up a straight unicorn as an SCP, it'll get deleted, and you really need to add something special to the article to get it put up. It's difficult, but the resulting articles are typically the better for this extra effort.
Except when you get a really obscure myth- to pick two which I don't think have been attempted as articles, the Nuckelavee of celtic folklore or the Yara-Ma-Ya-Who of Australia - the fact is that most contributors haven't heard of it before. So people will tend to like the article either because they mistakenly think that the myth is the author's work, or they enjoy it because they've been introduced to a cool new legend. These articles can end with quite a lot of praise, except the author's creative input to the article is actually fairly minimal.
Again, it can be done right (SCP-1036 is an obscure myth, and it's one of my all-time favourite articles), but when writing something based on the less well-known myths, it can be easy to get lazy and just restate a legend instead of coming up with something original.

SCP-0136 is an obscure myth, and it's one of my all-time favourite articles…
…That's been deleted.

SCP-1440 is somewhat based on an existing Russian folktale, while still being a well received article. It's a fairly obscure folktale, however.
My feeling is those are a real bastard to write well. When we had the SCP-1000 contest, I tried a couple things and couldn't do it. You need to take the object, or creature, or story, and add a twist that makes it more interesting, and not a straight-up SCP-ification (unless it's for Project Crossover). It's not easy to do that for a mythos that has already been well worked-out in other literature.
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