This is an arena for custom bosses, it comes with a preset custom boss fight using command blocks, the arena has a few command blocks with preset arena settings, the entrance can be blocked, weather and time change. There are also some "optional boss settings," this command block will actually give the player a custom boss bar. Some of the command blocks have specific coordinates, if you want this build in your world you will have to update the coordinates manually in the blocks. The first two command blocks control the entrance with a fill command and the boss fight command block has summon coordinates to the middle of the arena. In the command block that gives the player a boss bar be sure to replace "Your name here," with your gamertag. In the shack in the arena is a chest with some (2 items) custom loot, the shack can be opened with a key (lever) that will drop from the preset boss if it is killed by the player, the preset boss has 1000 health but not very strong attacks, both of which can be changed in the command blocks behind the control panel wall and the boss summoning block. Around the arena are eight lightning rod pylons. All commands in the build have been double checked and are working as of 1.20.1. Included in the download is the world file and the schematic.