At the pet shop in Falconreach talk to Aria's grandmother. Go to Critter Cave and defeat the creatures that are guarding it and then search for Aria inside. When you find her defeat the spider until Aria tells you that it is her pet. Press 'Continue' and Aria will join your party untill you are out of Critter Cave.

To do this little trick you need to make a Level 1 character at the Character selection screen and make a note of it's ID #. Then go to the arena and enter the ID # you made a not of into the 'Battle ID' feature and keep defeating to get as many trophies as you want.

There are no cheat codes or passwords that we know of for this game, but if you would like an easy way to accumulate bags of gold, just keep repeating the beginner tutorial.