The Piece Editor is a tool in the workshop. You can set a piece's properties, e.g. density, friction, colour, and more. You can also access the Piece Creator, with which you can create your own pieces. It allows you to code pieces, add & color pieces, copy the pieces' code and so on... Use this to make unalike pieces or hard-to-make pieces, and more, just use it carefully, it can glitch!