Plethora is a mod of many things, from simple create mod ores in the nether, to a whole new processing line for an upgrade to netherite, to even a whole ass entire new dimension, this mod has practically anything you could want. A full feature list and how everything works is in the mod in the form of a guidebook in game, and all you need to do is dive in and learn
You need to have create installed to use important features, so please, be sure to install it.
