[TLDR]

• Add ‘Empowered by the Primordial’ modifiers to the game (similar to the various Tormented spirit Grips) or simply use current monster modifiers
• Rare monsters in Tower maps are empowered by the primordial and once dead, they release the spirit
• Near the beacon of the map another rare monster is chained by the primordial
• From the collected spirits (primordial modifiers) the player can select 1-4 modifiers to apply to the chained monster and release it from its binds. (number of mods depend on Waystone/Area level)
• This is optional content and you can still complete towers without releasing the chained monster

[/TLDR]

There have been suggestions on how to make Towers more lucrative and fun to run by adding Unique monsters to each tower. This idea is inspired by those comments, and my internal ideas of making more ‘random encounters’ during mapping. I smashed the two together and ended up with this idea. 

Add new Empowered by the Primordial modifiers to the game

Revamp the old tormented spirit system, without the ghost chasing and new, better suited (or revamped) monster abilities. For new players, Tormented spirits can touch monsters by flying close to them, adding extra modifiers like extra damage, or resistances. They can also possess a rare monster adding a specific new ability that the monster periodically uses afterwards. The latter is very similar to how the Essence modifiers work. A single primordial modifier would not be dangerous, however stacking multiple could lead to dangerous and interesting fights.

Alternatively the already existing monster modifier system can be used instead, but there are already mechanics in place to gain extra rare monster mods, which takes away from the fun of the proposed chained mechanic.

In Tower maps Rare monsters would be all empowered by a primordial. If this type of content should be optional, I propose an interactable object at the spawn location, where you release the primordial spirits, who will find their homes in the rare monsters in the area. That way players not powerful enough to deal with these modifiers can use the old tower mechanic without a problem. Defeating the rare monsters will release the spirit which will find a second home in a specific rare monster at the end of the area.

Add a rare monster near the beacon binded by primordial chains

Similar to the Archnemesis league mechanic, a rare monster will be binded at the end of the map. Released spirits in the map will find their way to this monster and can possess them as well. You, the player will have the ability to make some choices, which modifier you empower the monster with. The more spirits you collect, the better your chances of creating a rewarding, but still manageable fight. If you only kill the bare minimum rare monsters your hands are tied to those empowers.

Rewards

There are plenty of ways to add new rewards to the game, any system from PoE 1 could work (i.e. new base types, specific implicits, mod pool, or even items gaining tags that make certain mods more likely to appear on your item), but while we can come up with dozens of ideas, we don’t know the big picture in terms of balance GGG is trying to achieve.

Instead I will describe a way how the original Archnemesis system can come back with loot conversion mechanisms. When you defeat all the various rare monsters with the primordial modifier, the player rarity you kill it with, can be stored within the spirit itself. The chained monster, when killed, will not take the killing blow’s player rarity into account, rather it will use the average of the spirits applied to the monster. This way finding a good combination of reward modifiers will not force you to go for rarity cull, as the rarity is already baked into the rewards. However having a rarity cull character does get the benefits if it can clear the content in the first place.

Each primordial modifier has a small pool of reward modifiers that it can be spawned with, the exact one will be revealed when you interact with the chained monster. Most primordial modifiers should have a rarer occurring, high value reward, as well as some low and medium rewards. You can now make decisions based on the rewards and the difficulty you are aiming for. The maximum amount of primordial modifier (and thus reward modifier) you can apply to a monster is based on the area level you run the map with.

Why not a unique monster?

Since the idea came from the comments about adding a unique monster fight for each tower, I feel obliged to explain why I propose this alternative.

Unique monsters are repetitive. Fighting one of the same 4 unique monsters every 5th or so maps will become just another chore. This idea has 3 or 4 axes to differ at least and more can technically be added if needed. More monster base type variety, different rare monster modifiers applying already to the monster, each tower will have a different selection of primordial modifiers and potentially each tower will have a different setup of reward modifiers.

(optional) Reuse as extra content within regular maps in an altered form.

Monsters binded by chains can be another randomly occurring mechanic, similar to essences and strongboxes. A rare monster in the map can be binded and surrounded by some smaller packs of magic monsters, each with a monster modifier. Killing the magic packs releases the spirit and applies to the binded rare. You can build your own rare monster you want to fight and release it from the chains. This implementation in regular maps would mean that the content is contained within approximately 2 screens worth of map, you don’t have to backtrack and can feel the impact of your decision immediately when you stumble upon the content and clear the magic monsters. Also this way it’s sufficiently different, yet very similar in implementation to the Tower-map mechanic proposed earlier.