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1. You can find them in Daily Chance or you can purchase them from other users or at the Casino.
2. They are used to purchase bacchelors robes and hat from Edmund. You can exchange them in his shop, H.R. Wesley. Just click the Credit Exchange under his picture in the shop.
3. Signature pets, basically. You post a code with a picture, occasionally the picture changes. Sometimes you can 'breed' them with others to produce another picture, sometimes you can click to 'feed' them. Sometimes you can RP with them in forums. Depends on who made them and how many users have purchased them. There's many feedable/breedable guilds, and you can also purchase them from minishops in the forums for varying prices- though honestly, I never saw the appeal in spending gold on anything for my signature other than avatar art.
tl;dr a breedable/feedable is a picture of a creature you put in your signature that has some sort of interactive feature, such as 'click to feed' or 'fill out this form to have your creature mate with another users creature.'
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