Phoenix Adventurer’s Boxes are a type of Lootbox that can rarely drop from any monster. They were introduced in the Meownt and Candy Fishing Edition patch.
They used to drop commonly from killing enemies, and be put in a ‘rotation’ between it and other Adventure Boxes, changing monthly. This was later changed so that all adventure boxes could drop rarely.
This chest can either drop Truefire Pheonix or Balefire Phoenix rarely.