Along with new fighters, stages, and Amiibo, Nintendo has released a slew of costumes for your Mii Fighters, which you can see here:

 

 

The costumes are available to download right now, and cost $0.75 each ($1.15 if you want the Wii U/3DS bundle).  If you want all of the costumes in this second wave, you can purchase the set for $6.00 (9.20 for the Wii U/3DS bundle).