At what level can you add an archetype to your character?
I have a level 2 Barbarian and I just found the 'Mad Dog Barbarian' archetype that I would love to try out. Can I simply add this to my character sheet and pick up a pet for him?
Archetypes are chosen when you pick the first level of a class. You cannot add them retroactively. Of course, if the GM allows it (especially since you're only level 2), it would be ok.
Actually, you should look over the archetype to determine the earliest level at which the archetype has any effect at all. Without retraining, you can select an archetype at any point up to the time you reach that level. Thus, if an archetype does not modify or replace anything that your base class grants at 1st or 2nd level, you really do not have to commit yourself to the archetype until 3rd level.
In the case of the Mad Dog, you are just slightly too late unless your DM is in a good mood. The first core class feature lost is your 2nd level rage power. If you have played at 2nd level, you have presumably selected and started using a rage power, so technically retraining (or bribing your DM) would be required to replace it with an animal companion.
Fair enough, I won't be losing to much to re-roll this Barbarian as a Mad-Dog and catch up to my son who will be a few scenarios ahead of me. Thanks all!