The concept:
Elevator Pitch: An entity(Female humanoid) that is known to the public to kill dogs (domesticated and wild). It will also kill any person that tries to stop it from eating. Never captured due to it always being too fast and it seems to plan its routes of escape early before attacking the dog. Before attacking, a bell will be heard and the dog will bark for a long time.
This doesn't feel like much of an anomaly, more so a random person going around and killing dogs?. The skip doesn't have any clear motives, interactions with the Foundation or much of an anomaly to begin with. Currently the skip seems to fall into the "X-men syndrome" cliche, this is where the article is more focused on giving the skip powers and cool/weird abilities, rather than tell a story about an anomaly.
"Speed" feels more like a superpower than anything. In the context of an SCP, it feels out of place and considering how much its already been used, it feels a bit generic and unoriginal. The effect here feels a bit disjointed, considering there isn't much of an explanation why the skip can do this, and how that relates back to the dogs. Overall, this effect feels like a quick way to explain why the Foundation can't catch the skip, as it doesn't have around it narrative or concept wise.
-As a small side note, How exactly does the public know that this person kills dogs? its not given much of an explanation, what causes the detail to feel unnecessary.
Overall, the concept doesn't have much to stand on, considering the pitch is relying heavily on the skip killing things for audience attention. Personally, it really doesn't keep my interest, as there isn't much else that makes it stand out from your run of the mil murder monster. -there are many ways to make something interesting without it being 'dangerous'.
-Do note that humanoid SCPs are among the hardest to pull off, as they prone to falling into cliches. Considering this is your first skip, I would recommend you look at something a little less difficult to start off with.
The narrative:
Central Narrative: A dog killer is known all throughout the west of the world(North America) the Dog killer was practically unkillable until someone did kill it after seeing it eating his pet.
This isn't much of a narrative, more so some general information on the skip. There isn't much of a setup, middle act or payoff. I'm unsure of how the Foundation find out about the skip, what they end up doing and what happens after the Foundation has learnt about it.
In any case, I would highly recommend you start developing a narrative, as they keep audience interest and can further explain the skip. Modern audiences tend to favour narratives, which has more or less lead to them becoming the standard. -You would have a much easier time getting a concept off the ground if you had a narrative to accompany the skip.
Hook:
Hook/Attention-Grabber: The hook is this was not the only dog killer and there are more spread across the world, once one is killed more make themselves known. The foundation was only made aware of One, and soon they will learn of more spreading quickly over the world.
I'm a bit unsure on this, it leaves me more confused than anything, I'm not sure: why exactly is this happening? why are they killing dogs? where are they coming from? how does the Foundation know that they are anomalous to begin with? (the act of killing a dog isn't anomalous, its morally bankrupt and heartless, but not anomalous).
Red or green?
Due to my afore mentioned concerns, no Greenlight. I would recommend you look at shelving this time being, as there is a sizeable amount of work that would need to go into this. the concept in general doesn't have much behind it, the "dog killer" aspect feels like its been added in for shock value and there is no real narrative to go off of.
You may find the following links helpful:
http://www.scpwiki.com/how-to-write-an-scp
http://www.scpwiki.com/yourjouney-part-1 - the other two pages are linked at the address.
If you would like me to give this further advice/feedback, then feel welcome to shoot me a PM or ask via IRC. response times generally range from 2-12 hours over PMs. If your looking for additional critiques in general, then I couldn't recommend the Butterfly squad more:)
