a grotesque rat  

I recommend killing the thought destroyer first if she's up. I was standing inside the hideous rat's house, a few seconds away from engaging it when I got a message from the thought destroyer. She ran in the house and attacked me. So she must have a fairly large aggro range.

Kill the single mob in the first room. Now, it's helpful to have lev on. Go over and stand at the top of the steps on the left, the hideous rat will be there with a mob to the left of him. Unless you can pacify you will get 2. Get yourself in a position to aggro on them without going in the room. Try leving over them a little and then pull back before you drop into the room. Or if you can get yourself into a position to cast on one of them by standing on the table in the first room, try that. You should get just the 2. CC the one or fight them both. As a 70 ranger I didn't have much problem downing them both at the same time.

Good xp for nameds in hate, got warrior mask twice.

Someone farm this guy and find out what his rare is. I'm really curious now.
Hes not much different than any tier 2 monster but he can have 1 to 4 adds when you pull him without Pacify (Mage style) so be ready for a good fight if you're solo. You can see inside his house from where the corrupter of life stands and his PH is a vile rat.