Apparently you can cut of its tail but I tried numerous times and couldn't do it. There's videos out there that shows how to do it but in my multiple attempts it just never happened that way. It's also possible to shoot off its tail from down in the middle of the bridge with a shortbow. I did that the last time I played but this time I'm not upping my dexterity and will not be doing that. You can get a cool sword doing that though!
But yes that same method to cut of its tail also shows you how to get past it. Stand at a certain point and then run to its right and straight for the bonfire.
I know Beo said not to use guides but when I get stuck I google it.
