From Outwar Wiki
There are many different mobs in diamond city, they range in all types and levels big and small. Some drop special items for Quests. There are others that need to be killed in certain amounts to meet a quota for Quests. ie. 10/50 Large Rats Killed.
There are many types of mobs, here are a list of a few of them.
Regular mobs are the creatures that you see all around DC. After you kill one of these mobs they will re-spawn in about 5-10 minutes.
Rare Spawn Mobs
Spawn mobs normally appear grayed out and can not be attacked. The only way to kill a spawn mob is by spawning it! To do this you must kill all other mobs in the same room (room, not place) as the spawn mob, but still after killing all the other mobs sometimes he doesn't spawn, in this case you have to keep killing the other guys in his room until he does spawn.
Example: Bruno 
TIP: Apparently there is a logistic sequence to kill the other mobs
User Spawn Mobs
These are mobs that appear only for the current player, usually as a result of a quest
Special mobs are unique to the time of year and are a fun way of incorporating the outside world with Outwar. Around Christmas time Rampid will release a new quest that has a special Christmas mob in it. These mobs only stay around for short period of time and the quests normally produce a special present ie. Wrapped Gift, Candy Corn.