The Essentia mod aims to add two opposing progression trees; the domination-focused school of thaumatology, and the hamony-focused school of witchcraft. As you grow in power, you learn to manipulate the metaphysical building blocks of reality for your benefit.
Stipulation: Essentia is the metaphysical building block of reality. All that exists is infused with essentia, and all that is infused with essentia exists, to one degree or another. Essentia comes in different flavours, or 'aspects'. What aspects an object contains is determined by its nature, and by altering the essentia composition of an object, its fundamental nature can likewise be altered. Before the discovery of dimensional travel, essentai could not be found in its pure form in our universe. It is unclear if it existed here at all. After the cataclysm however, object and creatures of pure essentia can be found, most notably during portal storms.
Laws of physics, the primordial bedrock upon which our understanding of the natural world rested, have shifted and heaved into an unfamiliar landscape. Yet as your ancestors once did, you too can learn to understand the laws that govern reality. And with understanding comes power. Though carecul study you can learn to extract essentia from the world around you and use it to alter objects in interesting ways. Thaumatology focuses on crafting permanent items and using a vehicle. It is inspider by Thaumcraft.
Witchcraft is a collection of a range of harmony-orientet magical diciplines that involves barganing with supernatural forces for power. This school is inpired by the Witchery Minecraft mod, along with summoners from Pathfinder and warlocks from D&D 5e. The school focuses on a sedimentary lifestyle, where the player will want to have a stationary home to build altars, summoning curcles, and so on, and have fields planted with mystical plants. Items of power tend to be fairly cheap consumables.
In game, your progression in witchcraft is handled through a cat familiar that you learn to summon. Doing quests and favours for them earns you reward points that you can use to buy knowledge and power.