Preface: I'm a bit of a stickler for Cosplay builds being done right, even with all their disadvantages. IMO if you're going to Cosplay don't be half arsed about it. Pet peeves are things like Ornstein builds with Grass Crest Shields, and Artorias builds using Dark Magic
There's Cosplay, then there's just wearing the armour and using the weapon and calling it Cosplay.
When I Cosplay I prefer to try to get it right, even down to the roll speed. Things I do allow myself leeway on are rings, if I'm doing an Artorias Cosplay I won't wear the Abyss ring as it has no effect on the visual aspect of the build, which is everything.
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Ok, now that that's out of the way, here's my Artorias build, and some others that I've used/are using.
Artorias as you fight him: http://mmdks.com/2t12
I use Karmic Justice to mimic his powerup and explosion, and it also has the added benefit of preventing people from just wailing on you since you have no shield.
Bare hand parries for those that do mash R1 (if I can pull them off), SL120 would have 40dex for added damage.
I eventually took it to SL150 and has some success hosting in the Forest, using this build: http://mmdks.com/2t1a
With this I could RP Uncorrupted Artorias using both the Cursed and True version of his sword, and his shield, along with a changeover build where he used the Cleansing Shield and Abyss Sword and Wolf Ring, and also the Corrupted version with bare hand, fast roll (swap Wolf for Havel's), and Abyss Sword.
All in all it was a fun build, shame the R2's on boss weapons are so slow, the only good one is the 1HR2 of the Abyss sword, which still doens't even hit twice like the Halberds swing even though visually it does hit twice.
I had great success Sunbroing as Ornstein at SL60 outside of Artorias's door, had to two hand the Dragon Slayer Spear so I could have enough faith for Great Lightning Spear and still be able to mid roll, but that was alright as I didn't have a shield anyway, can't remember the exact build, I lost that bunch of characters when I formatted my comp. Never died with it though even on Kalameet, and only lost a few battles against Arty due to the host being squishy and not knowing how to heal.
I've had some great fun with my Xanthous King Jeremiah build, not good for hosting as you run out of pyros pretty quick, but great fun for invading as a red (like he does): http://mmdks.com/2t1y (vit/end might be off, can't remember exact stats). Crown is a little annoying as you can't see much where you're aiming, no black flame as Xanthous doens't use that, I should put more Chaos pyromancies in there but they take up too much of my spell slots for not enough casts.
Shiva is fun too, the Mura hits like a truck, make sure you've got fast roll though to make up for the average poise.
Stone Knight was great fun at SL55, fat rolling like a boss, TWoP from the Sword was handy as well, also if you do a 1HR2, then another 1HR2 the second one will swing a lot quicker nad flatten people. Not many people seem to know this as throwing out a dummy 1HR2 would 99% of the time lead people to come in for a hit, in which cases they would get flattened
Build: http://mmdks.com/2t1z
In fact making a high level 40/40 quality build so you can RP most things is a great idea. Shiva, Darkwraith, Kirk, Gough, Orn, Stone Knight, Silver/Black Knights, Crestfallen, Ricard, Lautrec, Baldur Knights, Hollow Soldiers, Tarkus, Havel, etc.
Also I really like Mildred too, but more for Co-Op than for PvP. SL30, Flash Sweat. Run in, hit Quelaag a few times then go play in the lava. Come out and hit her a few more times, recast FS then go play in the lava again.
Domhnall is useless though, fun for a playthrough, but not for PvP, even with Gold Pine Resin on the sword it's still weak sauce and has no range and is heavy. Looks awesome though imo, especially the hilt.
Other fun ones are Shivas bodyguard (dex/pyro with a katana and ninja flip) and Kirk (if you get invaded by a poiseless low level guy just roll into them until they die of shame haha) and Gough.
For Gough though I'd recommend a very high level, as you need lots of endurance, health, and fast roll.
Siegbro is also awesome, I don't have a build for him atm but WotG, Emitt Force and a few other defensive ones, along with a Zwei makes for lots of damage. Mid roll if you want to cheat a little
Some pics and a vid I have uploaded atm:
Mildred (I did cheat a little with this one using the Wolf Ring at parts):
http://cloud-2.steampowered.com/ugc/921242003828297828/2F9FD02A4AD793A9267C0E160527F55695B13B5F/
http://cloud-2.steampowered.com/ugc/921242003836306502/270295EE565A025B77893112B92FC17A4D4D0DA9/
Bonus PvP shot, started with 0 souls, did this well before I died, first death was just after this screencap:
http://cloud-2.steampowered.com/ugc/921242003887852508/48FE9649D31BC7684753B76EBEDE415D4A1E5C85/
Stone Knight Forest Hunter: http://cloud-2.steampowered.com/ugc/867219838524181770/39F39D70DB699F516E1D5D1AEE04DA46CAEE11D1/
Gough Forest Host/Gravelord: http://cloud-2.steampowered.com/ugc/866090369262631906/35EB25D6DCF651E9670561F888348A56066F97DB/
Ornstein Artorias Sunbro (SL60):
http://cloud-2.steampowered.com/ugc/921242735968133757/A093F469F46B2FAAB06DD31706D9A6B8C30225C6/
http://cloud-2.steampowered.com/ugc/918991495553905908/F7270F1B007DF8F04C41AE72184DA7C3559D8D59/
Artorias, first of my cosplays:
http://cloud-2.steampowered.com/ugc/921240396466236980/8729A0BCDA418FB76EB94B43441502948581AF29/
http://cloud-2.steampowered.com/ugc/921238949586499305/406F79E882ACEBEB38510B146176055EDDB7A715/
http://cloud-2.steampowered.com/ugc/921238949570268226/EE0B08A4B880AC8D471E1AA54958A5DE69976BDC/
http://cloud-2.steampowered.com/ugc/921238949575930020/E80D279285F04C67491C983DE306045D012B0558/
Xanothous vid: https://www.youtube.com/watch?v=mYXr8z1gr-4
Domhnall: http://i5.minus.com/iN1AB4XXZSbeH.png
http://i7.minus.com/ibiyAYWMxbaAim.png
Gough Vid: https://www.youtube.com/watch?v=jkFYDgxbG8w