Oh, you know the worst kind of griefer? Those with Havel's armor, and that weird repeating crossbow. They will fuck you up hard.
I had a pretty good fight with an invader, and I was winning after a successful riposte, but he got this thing out and one shotted me from full health to dead with that thing...
I am still too scurred to regain my humanity. I am quite stuck being undead since I would freak the fuck out if I got invaded :p Only issue is that I read I might miss some optional story elements that can only happen when alive.
[EDIT]: Just beat the hell out of the Capra Demon, now from what I was reading here I was dreading the encounter and nervously twitching when I was contemplating crossing the fog gate but he went down on the first try.
Maybe it was just my upgrade grinding speaking but I had alot more problems with the gargoyles, they took about five attempts. What I did was cross the gate, make sure to instantly raise my shield, run straight forward and kill the dogs (I used the spear attack that you can use with your shield still raised.)
After they were dead I kited the Capra up and down the stairs by running up it and as he was following and about to attack, I raise the shield and jump down, wait for him to jump down, attack two or three times then run up the stairs and repeat.