Download the spigot.jar version 1.12.2 and rename it to "spigot.jar". Create a folder for your server. Build the project in IntelliJ IDEA , add spigot.jar to library and build the plugin to jar. Paste the output jar in "plugins" folder in your server folder.

Double click on spigot.jar and change "false" to "true" in the eula.txt file. Click on "start.bat" it will make you all the file you need. In Minecraft connect to localhost server, first every player die and after they respawn you can't place any block if the game is not start. When all your friend (ssh tunnel for public server ex: ngrok ) are ready tape in the console "/start" the game will start, zone minimize every seconde. If you die you will be in sectator mode and if a player join the game when it's running he will be in secptator mode too. You can tape "/stop" for stopping the game ("/pvp" for all information). The last player a live win the game (auto restart).