RPG custome monster spawning

Im making a RPG server based on World of warcraft. This plugin need to remove normal mobs from spawning and let me make custome mobs and areas they spawn in. A gui wude be nice but is not needed.

The plugin also need to look on a timer if anny mobs are killed and if the amount of mobs are less the the standerd it needs to spawn the mobs that are missing. i have a huge map so this plugin needs to be able to have aalot og mobs and areas that it controls and don't lagg the server.