A plugin that lets you be on the good or bad side
On good side you can ride on a sheep!
And the bad side a spider that can climb!
The sheep can eat grass and then get superspeed :O

A plugin that allows you to add any effect to any mob/weapon/entity within a certain world or area.

A good planes plugin with upgrades and different types and a car plugin with upgrades and different types

or a plgin that allows the player to sprint much faster

a good car plugin with a bunch of different types of cars, a company plugin that has different ranks throughout the company and is fully customizable, a stock plugin to go along with each one of the plugins, a cellphone plugin that allows you to text and call from your phone on the server and your real phone, and an economy plugin that has credit cards, atms, and goes along with each of the plugins and has different currencies.

a plugin that adsobes far away items like 40 blocks away someone died the items would go to the player like exp.

One that undos other peoples worldedit
like
//undo [NAME]

a plugin that you get the persons head in your inventory when you kill them