The Umbral Crux

A biome, both warped and defined by its excessive amounts of umbral energy. It has dangerous plants and even more dangerous mobs. But if you keep to yourself, you'll be fine.
New wood type: Hornbeam
New stone types: Phyll and Biship
New mushroom: Egoshroom
New fluid: Piu (gives regen but nausea too)
Many new plants: Eilys, Wailing Vines, Stalbarbs, Starchids and Riska

And a mist that swirls around the biome.

Wisps - 

These ethereal beings are the souls of villagers who couldn't move on. They now restlessly zip around the weald, overflowing with Geist energy.
Dewlad -

These trans-mutated endermen lost their ability to teleport but have found different ways to disappear. They can blend into the weald's mist and turn invisible when hurt.

Shade -

The result of condensed nightmares in the physical world. They fly around swooping down to scare other mobs. However, they don't bother humans but will lash out if attacked.

Apus - 

An undead variant of cow. They have a long coat of fur on their bodies and their flesh is stinky (but it's good meat).

Clay Golem

A summoned golem that has only one purpose. To kill all monsters in the area. However, they are not loyal to you. Only your binding covenant makes them listen to you. If you give them a reason to turn on you, they will.

Aphoticite, a powerful new ore is the condensed form of the first Ender Dragon's aura and currently, the only form of umbral energy in the overworld. It's used heavily in the process of Artifing as both a power source and an ingredient. Here's more on that.

Artificing is a form of magic shunned upon by mages and despised by clerics. It utilises a dark power to empower/bind magical power to objects. This is a form of alchemy so specific requirements are needed. First, you need fuel (an Umbral Core) to power the reaction. Next, you need a catalyst (a mob sacrifice in the form of a drop) to determine what powers/effects will be added. And lastly, a base (a plain item that the power will be applied to). The Artificing Table is made with planks in a U-shape at the bottom, an umbral core in the centre and three purple carpets on top.

These are magical items imbued with dark power to carry out specific tasks.
Golem O' Clay: 

Left-click to summon one Clay Golem. It also provides you with a Covenant to uphold your bond. Dark powers are unstable after all. Who knows, if you anger it, it could attack you.
Made with Clad (Base) and Undying Shriek (Catalyst)
Chains O' Dominance:

Left-click to chain up your opponent with the fiery bonds of dominance. Once trapped, they'll be unable to move, see or attack for some time. But act quick, it doesn't stay for long.
Made with Chains (Base) and Blaze Rod (Catalyst)
Shadow Mask:

This boon gives you spiritual sight. As long as you wear this and sneak, you shall see the world in the brightest light even in the darkest night. No mob can hide from you as you see their soul as clear as day.
Made with Gold Helmet (Base) and Moonglow Fin (Catalyst)
Cloudy Cleats:

This boon allows you to float. By pressing your "X" key, the wind will lift you up. But with each tick of flight, your little durability decreases. It's recommended you savour it by using small double-jumps lest you fall to the ground.

Made with Gold Boots (Base) and Milky Pearl (Catalyst)

Two music discs have been added...
Void by Cretayu
Link to Social Media/Channel:
https://freemusicarchive.org/music/Pedro_Santiago

Radiance by Siddhartha Corsus

Link to Social Media/Channel: https://freemusicarchive.org/music/Siddhartha
Original Name: O' Radiant One (changed for easy reading)