Proposal: The Obsidian Spire (High Effort)
Magoc has begun walking It's path towards twisting and bending humanity to It's will. It is a mighty demon to be sure, yet It's followers show a significant degree of mortal ineptitude that could compromise It's plans and provide cracks for the blessed Heliel and her forces to take advantage of.
Heliel's cult was well-trained and well-equipped. They had specters as scouts, proper officers, and workshops. Healers allowed them to crash upon It's own followers as waves upon the sands, withdraw, and crash once more. While Magoc's followers have a clear penchant for the more subtle arts, the art of war has proven to be just out of their mortal grasp. And so it is that Magoc harnessed it's energy to pull a massive black tower from the earth itself.
The Obsidian Spire is a manifestation of Magoc's will. The sleek, black tower, seemingly carved from a single piece of stone, will grow and expand as needed. Currently it juts above the rest of The Forgotten City as a monument to Magoc's power, the sun and moonlight reflecting off of it's seemingly edgeless surface. In the center of the Obsidian Spire and running the entire length from top to bottom (and beyond that) is a magma vent filled to the brim with molten rock and constantly spewing smoke and ash. Within it and ringing around the magma tube are three distinct sections (from the inside) with separate roles.
The Black Library is where the nerds scholars and scribes study and write. It is the base of the Obsidian Spire and is itself dozens of meters tall. Shelves ring around the walls filled to the brim with books and tomes pulled from the aether filled with arcane and ancient (to the mortals) knowledge. Centered around the warm walls of the magma vent are the Inscription Tables, where those who would study and utilize magic, alchemy, and the Language of Inception are able to work and research. Librarians, shadows tied to the Obsidian Spire as much as the Spire is tied to Magoc, watch over the mortals and provide It with up-to-date information on the progress of the scholars there. Librarians will tend to the scholars, guiding them to books that may aid them in their current pursuit, whatever it may be. They are very proud though, and will drain the life of cultists who show them, the Spire, or Magoc disrespect.
The Caster's Chamber rests below the Black Library, accessible by one of four stairwells positioned along the outer wall at the four cardinal directions. While the Black Library is fairly open, the Caster's Chamber is a series of winding hallways and individual rooms where the magically inclined can acquire more practical training. The rooms do not have roofs, and instead are open to allow the Manifested the ability to observe and train the cultists trying to work magic. Manifested are fragments of Magoc who have bodies unlike their Librarian kin, but are still tied to the Obsidian Spire as they are. Manifested train larger numbers of Cultists at once - the individual rooms are more to contain accidents than anything else. This chamber is also a couple dozen meters tall.
The top of the Obsidian Spire (and will remain so - additions to the Spire are seamlessly added between floors) is The Crucible. It is here that Magoc's warriors train, having to first combat the stairs upward and then practice their martial arts while completely exposed to the elements. Cultist Warriors are forged here. As with the other areas of the Obsidian Spire, the Crucible is watched over by entities of the Spire known as Magots. They bear a remarkable semblance to Magoc, though they lack the horns and smile, and speak in common tongue. They utilize their fraction of Magoc's combat prowess to improve his warriors. The Cultists who train here must endure wind, rain, and the everpresent blinding smoke and ash (dependent on the direction of the wind), all the while avoiding either inner or outer edge lest they fall to their deaths. This makes situational awareness as much of a priority as a sharpened blade.
As Magoc's influence spreads and It's power grows, so too will the Obsidian Spire, until it pierces the very heavens itself. A war has begun, and while the Angel Heliel has landed the first blow, it is Magoc who will strike the last.
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So a summary of what I want it to do so Nuke doesn't need to guess because it's definitely not 100% clear in the write-up.
-A badass tower
-General boost to knowledge and skill with the infernal arts as well as the mortal art of Alchemy
-Increased magical capabilities in and out of combat among our spellcasters
-A badass tower
-Unit: Cultist Warriors, Cultists who've been broken and reforged to fight more effectively for Magoc in less than ideal conditions
-Multiple types of summons (that are bound to the tower and so cannot currently be used) that provide experience for both incorporeal and physical manifestations with a wide spectrum of skills
-A badass tower that can be modified through designs or revisions depending on the scope of the addition.
Sidenote, the Library could be a nice lure for those nerds in that tower nearby.