Pink Bear Jelly Party Hat is an S-grade treasure that can be obtained by purchasing Supreme Treasure Chest. The "All-Pink Bear Party" effect it shows means that when you pick up an All-Bear Jelly, there is a chance that it will generate Pink Bear Jellies instead of the original Yellow Bear Jellies. Upgrading the treasure increases the chance that the Bear Jelly will be Pink.
Previously, this treasure can only be obtained from gaining 2,140,000 points using Pink Choco Cookie during Pink Choco Cookie Commemorative Event. That event was specially built for Valentine's Day 2015 (as it is valid from 13-20 February 2015), and during that time, this treasure cannot be obtained from Supreme Treasure Chest. Now it is available in Supreme Treasure Chest.
This was the first time a treasure can be obtained from reaching a specific point or using a specific cookie.