|XP - ?|
|Drop - Coal|
|Health - ?|
|Attack - 1/2 - 1 heart|
|Spawn - Villages, etc.|
Rats are neutral mobs that become aggressive at low light levels. Similar to Vanilla Wolves and Zombie Pigmen, they are Pack Mobs, so will attack the provoker of any member of their pack. They are not very dangerous, however, and have low health and damage values. They drop Coal upon death. Players might make the error of mistaking them for Mice, (which run away from the player instead of attacking) which are much less dangerous and easy to kill.
A Hell Rat is a hostile mob similar to the Rat, found only in the Nether.
Rats can commonly be found in villages, so be careful when wandering around villages at night (Tested multiple times in a Mayan Village and Hindu Village). This is similar to real life, where rats tend to live in or near human settlement.
Source - Minecraft Forums