Love this little guy! He's so cute! Too bad he's usually hostile. Normal Rats need to be killed. Those spawned from the Rat Sword are your friends. Found in the Crystal Dimension!
There are options in the config file to make Rats spawned from the Rat Sword friendly towards other players and pets! By default, they are hostile to everything except you and your own pets.
How to Kill
Found: Deep underground Termite Crystal Dimension
Drops: rotten flesh