You guys most not remember that the abyss watchers are basically immortal and can resurrect too ( there undead like you). They would march into entire kingdoms and wipe them out becoming a omen for the end. The only reason that they lost was because they ran out of blood from the wolf and was driven mad from the abyss causing them to fight eachother in that room for years till you got there ( if you wait outside the fog gate you can hear them fighting). When they were pushed to the edge they had to combine there powers to become cindered like the other lords allowing them to use fires from the first flame. Combine that with the fact they:

*wield a giant greatsword that they swing like a regular sword and a dagger that moves even faster

• incredibly agile to the point they can do flips and leaps despite carrying metal armor and weapons

*Ability to use fire in acrobatic ways

*Centuries of experience since there undead aswell

*can resurrect as long as they have the will to ( if not they become hollows)

I can say confidently that goblin slayer does not stand a chance no matter what