You can limit the number of entities it spawns. A single entity above a hacker's head is enough to make his head constantly lock up (unless something comes closer).Isn't that the plugin that you load into your friend's server to make it lag to death?
Who cares if Mineplex has it?Another suggetion... *YAwn* that yet AGAIN suggests to add bots. There are major flaws with this system, and let's be honest "you" haven't been thinking it, Mineplex has it.