I have a confession to make... So I'm in the Rat King Covenant, and I really, REALLY want to unlock all the doors in the Doors of Pharros. But the problem is to do this, you need Lockstones, and lots of them!
So what I've been doing is admittedly jerkish behavior... I wait on the catwalk above where the opponents spawn. Then as they are summoned, I drop off the catwalk, landing almost right behind them and catching them between me and the mastodon warrior guy. (That position also prevents them from going for the spawn camp / hide area in the doorway.) A couple of spells, and they are almost instantly dead, if the mastodon doesn't finish them off first.
It's not an honorable way to fight... I should feel guilty, right? But this person is violating our sacred rat grounds! Plus I gave him a quick, merciful kill. He didn't suffer for long. (That's my rationalization, anyway.) Plus I need those darn lockstones!