Board Thread:News and Events/@comment-26005122-20170430220219

Every month, for the Japanese version only, a specific selection of Tsums will be made available in the Premium Boxes, as opposed to offering every Tsum currently available. This will increase your chances of getting a specific Tsum you want, instead of a really low random chance among all the Premium Tsums.

The Tsums available for the month of May are: Any Tsum Tsum not listed will not appear in the Premium Boxes during the month of May. The change was likely implemented to help people have a better chance of increasing the skill level of a particular Tsum they want. 
 * Romance Belle
 * Romance Beast
 * Scrump
 * Lady
 * Buzz Lightyear
 * Dumbo
 * Tinkerbell
 * Cheshire Cat
 * Elsa
 * Flounder
 * Sven
 * Mater
 * Rex
 * Ursula
 * Genie
 * Fairy Godmother
 * Finnick
 * Scar
 * Mad Hatter
 * Crush
 * Cruella
 * Captain Hook
 * Moana
 * Hercules
 * Stitch
 * Marie
 * Woody
 * Alice
 * White Rabbit
 * Bambi
 * Miss Bunny
 * Maleficent
 * Ariel
 * Rapunzel
 * Pascal
 * Baymax
 * Belle
 * Beast
 * Surprise Elsa
 * Birthday Anna
 * Lightning McQueen
 * Randall
 * Jasmine
 * Pinocchio
 * Princess Snow White
 * Princess Aurora
 * Maleficent Dragon
 * Judy Hopps
 * Simba
 * Nemo