Where pearls come from.
Shelly shares shell loads of pearls.
Shelly was introduced during the March 2017 TradeFest.
How to get
Originally Shelly could be adopted via stickers won by completing random Bonus Tiers of TradeFest, and this was the main source of these stickers, but they were also sometimes awarded as a specific Tier prize (e.g. 3 stickers were awarded as the Tier 6 prize of June 2017 TradeFest).
Shelly stickers are no longer available in TradeFest Bonus Tiers. They are currently only available at the Pet Sanctuary Sticker Shop by purchasing Bronze or Epic Chests. Shelly requires 15 stickers to adopt.