End's Phantasm
I've always really liked the End dimension. I constantly waited for it to finally get updated and receive proper attention.
But that never happened. So I decided to do it myself.
The goal of End's Phantasm is to turn the End into a place that players actually want to visit and better integrate it into the main gameplay loop. Survival starting directly in the End has also become possible.
Shine bright, like the stars above!
Biomes
Dreaming Den
See this strange forest? Under the silent watch of the Fallen Stars of the End sky, Vivid Nihilium and Pream Trees grow here. The latter have yellow blast-resistant wood, just like Endstone! Their foliage also yields Pream Berries, which heal you when eaten.

Now let's look on the other side of the mirror. Below the Dreaming Den is the Underisland, which can be considered a sub-biome. The ceiling is covered with Oblivion - a strange void-corrupted moss that can be used as repair material for anything, and Oblivines. You can latch onto them to avoid falling, and they grow Oblifruits, which have a chance not to be consumed when used!

Finally, scattered both above and below the biome are glowing Crystal Spikes. They are mainly useful for crafting decorative blocks, but those below the islands have a chance to be Voided, which can be crafted into tools that mine faster as experience increases, serving as an upgrade to gold.
In this new place, two new mobs spawn: Crystie and Behemoth
Crysties are little crystal fairies with an explosive relation to End Crystals. If you dare to hit one, it will attempt to dive straight into you to explode in a sparkly bang, or simply when it dies.
Behemoths are lazy giants sleeping anywhere on the ground of the Dreaming Den. Be careful though, as getting too close will wake them up, and they're quite grumpy! They are immune to knockback and ranged attacks, but drop powerful physical-enhancing meat when defeated.
Acidburnt Abysses
Legends say that centuries ago, when more Dragons ruled the End, one of them went mad and ravaged the starry landscapes below, destroying all life and leaving islands scarred with acid waste and cracks.
This, of course, is just legends and nightmares. Or is it? Dreams have proven to come true.

However, the environment adapted, growing plants made of obsidian and drawing nutrients from the eternal acid. Rocks formed from melted endstone, bringing and concentrating all kinds of minerals from within the islands. Formed a biome reminiscent of both the deepest ocean floors and the lushest jungles: meet the Acidburnt Abysses.
Below thrives a rather peculiar lifeform, here in the Choral Riff.
Corals learned to live off the void's echoes and whispers, gaining all sorts of musical properties. They can be used to craft Subwoofers to push entities when powered, and Choral Arrows to unleash the power of music right in your enemy's face!
General Changes
Progression
First of all, one thing might surprise you: when jumping into the End portal, you don't spawn directly on the main island, ready to face the Dragon (unless you turned this off in the configs).
This is because the portal now takes you to the outer End islands. To go fight the Dragon, you simply need to wander around a bit and find a Gateway that will take you to the battle. This simple but decisive change finally introduces the End into the main gameplay loop, allowing more casual players to explore it as an extra step before "finishing the game".
Because of this, Elytras have been nerfed and cannot be boosted until the Dragon is killed. You can still enjoy gliding around, but it's not so overpowered.
Obsidian Towers
The Obsidian Spires around the Dragon received a slight redesign by having a crying obsidian gradient near the top. This doesn't do anything, but it emphasizes the magicalness of the Crystals well.
Some of these Towers also randomly spawn in the outer End as new dungeons. What's inside is still in development, but you can find nice loot and a challenging experience!

Compatibility
From version 1.0, Phantasm has automatic compatibility with virtually any datapack affecting the End, with special presets for Nullscape and Endercon.
Multi-noise biome sources will be modified at runtime so that the End Highlands biome is split equally between it and Phantasm biomes. Additionally, Raw Purpur and obsidian pillars on the Dragon's island can be configured to generate higher or lower to accommodate any generation settings.

Screenshot taken with Endercon installed, the datapack was not edited in any way
If you encounter any datapack that doesn't generate properly, please report it so that presets can be added.
Addons
Nullnite's Echo

Created by the amazing SashaKYotoz, Forge porter of Phantasm, Nullnite's Echo is here to fulfill all your wishes for amazing equipment in the End.
Go on a journey through the Underisland to find remnants of Nullnite, and use them to craft a powerful Nullnited Pendant capable of mastering the elements!
End's PhantasmZ
This addon adds level requirements for End's Phantasm weapons and tools to seamlessly fit with LevelZ. This way, you can add the End's Phantasm mod to your RPG modpacks without worrying about people skipping progression.