EliteLootbox is a customisable lootbox plugin that allows you to create lootboxes that are identical to a well-known server's lootbox feature.
This plugin comes with an in-game reward adder (Support NBT Tags) and it comes with a fully customisable percentage system.
How to add an item
1. Put the item you would like to add into the crate in your hand
2. Execute this command /el addreward <crate> <percent>