A new challenge has begun in Pokémon Shuffle in the Nintendo 3DS. This is the first of the Ultra Beast Challenges (UB Challenges). These stages require players to complete Stage 300 in order to activate. They don’t allow items and only can be played three times in total. This particular stage features Nihilego and is scheduled to run until September 3, 2017. These additions require the update version 1.4.20 to download.
Source: Serebii
Pokémon Blog 