City Boss Chests are items that can be obtained by defeating the George the Gorilla boss that can appear in Blox City. It, like other Main Hub boss chests, can drop gems, crate keys, hoverboards and a pet. City Boss Chests cannot be burned at the Incinerator in the Junkyard.
As of v1.103.0, this item can be converted by the Main Hub Gumball Machine into Gum. The exchange rate is 1:1.