Bosses are a type of interactive level that can be considered live puzzles.
The owner or another editor creates a large rectangle or square in the map to serve as the playing field, and creates a Gate (typically at the top) where the players can wait for the next round to begin. Bosses are usually accompanied by lobbies, where the player can practice various puzzles while they wait for the next round.
In a boss level, the goal is to be the last man standing. Prizes range from the Crown, to the level code or edit access, but the Crown is the most common. Typically you have to win a boss a certain number of times before the grand prize is given. This is controlled by a system of coins, coin doors, and gravity arrows. Boss levels involve multiple people trying to complete any of the level types listed here (as well as some Common puzzles) as fast as possible or before anybody else. Loss of a boss battle will often result in your falling to the bottom of the playing field, which may contain gravity arrows to push you back into the lobby. Unique to boss battles are active platforming, where if you aren't fast enough bricks below you start to disappear. Before the bricks disappear, the boss usually gives a warning by turning them red or another color.