Help, please identify this mob!

Hello, I'm new here and I don't know if this question has already been asked but I am on my first playthrough of Dark Souls and I'm at Sen's Fortress just about to take on the boss for the second time since I died on my first attempt. I was clearing out the area from the bonfire and I encountered a creature which I've never seen before after I killed a balder knight down a long corridor. It wasn't there before I died and I've looked for this mob on various lists of mobs, bosses and NPC's and can't seem to find it. This creature consists of what seems to be fragments of a pearl/egg body, crab pincers and legs, glowing tendril like things comming out of the top of the body and the body may have held a blue-ish like content to it. I do not know as I didn't get a good look at it when I was quickly killing it, this blue content dissapeared after it died. It dropped 1 humanity, about 200 souls and it's corpse does not dissapear. I innitialy thought it was something like the crystal lizards so I thought it would try and run away but this was not the case.
I am level 61 and this is my first playthrough. Please help?

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Thanks everyone for clearing that up for me! c:

This is a transient mob. They are very rare.
This means another player died and lost a LOT of souls or humanity in that location. Some transients run away, much like the crystal lizard, but many will also stay and fight, and do quite freightful amounts of damage.

That's called a Shadow Kingler, obviously!

Or a vagrant.

Sounds to me like a vagrant, see here (at the bottom of the link).

http://darksoulswiki.wikispaces.com/Online#Online%20Play-Vagrants%20(Also%20Known%20As%20Drift%20Items)

or here for a picture

http://darksoulswiki.wikispaces.com/Vagrants

I ran into my first vagrant while I was invading this guy's game in the catacombs. I messaged him and dodge his attacks long enough to show him where it was. A couple games later I see one in my own game in the Duke Archives. One hit took half my health, but when I killed it a I got a twin humanity.

i have 6 different chars in a lot of different NG's and never saw one of those

it does deem like a vagrant. and in my exp they are very very rare i have only seen 3 of them and i play just about all day everyday.

This weekend, on saturday I got one in new londo, and sunday morning another one at the Kiln. Two vagrants in a row.
Another thing, someone said long time ago that u had to be human and the boss had to still be alive in so vagrants can appear in your world.
That is not true. The one at new londo I was hollow, waiting to be summoned at the gate for the 4 kings fight, and I had already beaten them.

That's lucky, I've never seen a vagrant before.

Wow. I didn't even know this kind of thing existed.

I can imagine years ago, you meet your friends in school and tell them about this ridiculous enemy you just fought in the game, and nobody believes you for years.

There are actually 3 types of vagrants, good, evil and one "beyond". The one beyond is considered the rarest of the rarest. I had the incredible luck to encounter it in an other player's world I was invading (Demon Ruins). I never even heard about it that time. But I was just freaked out by the look of it and thankfully I was able to stand near and take a pic, it didn't actually go hostile or anything, just stood there looking quite awesome.

Spoiler:

I always get so happy when i see a vagrant...i didnt even know about them for the longest time. I have had the game since day 1 one and didnt see one till about a month or two ago. Now ive see about five. In fact i killed one in the kiln yesterday.

Darkson wrote:There are actually 3 types of vagrants, good, evil and one "beyond". The one beyond is considered the rarest of the rarest. I had the incredible luck to encounter it in an other player's world I was invading (Demon Ruins). I never even heard about it that time. But I was just freaked out by the look of it and thankfully I was able to stand near and take a pic, it didn't actually go hostile or anything, just stood there looking quite awesome.

Spoiler:

My god that is a horrifying looking vagrant, I'm glad I've only ran into one evil vagrant in the Painted World though.