Dull Bone Key  

 

This was first looted by our group off of the froglok, BoneCracker. This is not the only MoB to drop this key. This key is necessary to open the second door to Rathyl, once you are in the room in the basement which requires the Shiny Metal Key (off of the Ogre Guard Captain - I believe). Oddly enough, the Dull Bone and the Bloodstained keys both also drop off of the Magicians in the Shiny Metal key room.
Any Ogre guard has a chance to drop the Guard Keyring, which will open all of the nearby prison cells as well as a few other select doors throughout the zone.
The only other key in the zone that I am aware of, is the Golden Crescent Key, which drops off of Drelzna from both of her spawns in the zone. The Golden Crescent key opens the door on the other side of the underwater passage in the lake with the Froglok Ghoul