Creepersday is a plugin for Bukkit (Minecraft server).
All you need to run it is to copy the jar file into the "plugins" directory.

Then, start your server. Docs and default config files will be created into
plugins/Creepersday. Read the doc, modify your configuration and (if you are op)
run the command /creepersday-reload-config or restart the server.

Now, you can enjoy creepers' chase randomly :)