DLC will span a range of items, including costumes, weapons and enemies. The DLC will be more involved than simply hitting the download button though — players will need to physically unlock the content. For example you might need to beat a monster in order to lay claim to a DLC item.
Cool idea, but we're not sure how people will take to it. Kitase promised that players should expect a good balance between "price and quality".
The game's out next year.