Extras
Extras are additional abilities that function using their own costs and rules. Each extra has its own cost and requirements which can vary wildly, and each one explains the additional options and abilities that it grants. There is no limit to the number of extras a character can have, so long as they are able to pay the cost for each of them; however, because each extra usually introduces its own complications and subsystems, it is highly recommended for players not to begin with more than one, if they start with even that many.
Creating New Extras
Players who want their own unique ability can talk to the GM about potential additions to the extras; however, keep in mind that because stunts are versatile and Aspects are always true, a lot of abilities can usually be covered by including them in a stunt or an aspect. Extras should be limited to abilities that require some amount of mechanical changes.
For example, if you want your character to be able to talk to trees, giving them the aspect of “I Can Talk to Plants” or making a Treespeech stunt would both be sufficient; there’s no need to create an extra with its own rules. However, if you wanted your character to be able to transform into an animal, rearranging his skill ratings to suit his new form? That would be mechanically-oriented enough to make sense as an extra.