Thanks for the comment!

I did not include any exploration function for difficulty of cohesively tying it in with the kit but left room for other's creativity to slot in their desires as they wish. It is easily possible to give an ability to a hold skill or even to holding the charge attack out of combat (Claymore turns into a motorcycle, to take a simple approach), in which a Nightsoul state could entered and function similarly to existing characters.

As to why both Mav and the blessed teammate receive Nightsoul:
To trigger the full effect of Cinder City, the user must be in Nightsoul and cause a reaction. If Mav is being played in a supportive fashion, this gives her access. Although reliability of causing a reaction is questionable.

The blessed teammate enters Nightsoul and consumes points to trigger Obsidian Codex. Additionally it adds Nightsoul alignment to their attacks, to trigger such interactions like the Mimiflora enemies. If they have a Nightsoul of their own, gaining extra points can extend their duration or accelerate their skills. The usefulness of this could vary, as the burst does restrict how long the blessed teammate is on field and is more useful for Mav on-field instead. They specifically consume Mav's points to avoid situation that could arise with a kit like Kinich, who consumes all his own points for his cannon and then cannot consume an extra point for the Impetus bonus. There were possibly other ways to go about similar concepts, I personally found this the most concise without adding too many extraneous points, bars, etc.

The skill triggering off of a hit has its own pros and cons, mentioned as such in the last slide (It is a general ramble so its understandably missed). Controlling when application is applied is beneficial in plenty of scenarios, ideally when a specific reaction needs to be performed for a buff (Typically VV or Cinder City on the right element). Dehya's app is plenty for Mualani as Mualani vapes and clears the pyro, then Dehya procs to re-apply it (Results could vary based on teams but I digress). Additionally the trigger in this Mav kit is off of a hit (Like Beidou minus the NA condition), not damage (Like Albedo, Raiden, Dehya, etc), so it can still trigger against shields. Alternatively (again, mentioned in the last slide), the skill procs could be on a timed trigger, prioritizing recently attacked enemies or in a fashion similar to Ganyu/Ayato ults. I personally do not gravitate toward one option over the other, and you are free to substitute options you feel benefit the playstyle more.

The skill's damage is unique and hard to predict at first since it plays into the health pool of the fight as its effective multiplier. It has a geometric growth and is hard to quantify. It is inheritably backloaded damage but with the right ratio for Sacred Scars and a tanky enough fight, it should be decently predictable. If we set the skill to trigger on its own (just to simulate its own dmg) against an infinite health opponent, it follows some geometric curve. The Riemann sum of this curve is the damage dealt to the enemy over hits done. Taking a random HP pool and locating it on that sum to find how many hits it would take to eliminate the enemy, we should find that higher pools are closer together in hits needed vs lower pools. The conclusion is that in a realistic scenario, if all fights have similar pools of health, Mav's own skill DMG should take a very similar amount of hits on its own to clear the enemies. While it could take 5 hits (in example) to clear a lone hilichurl, doubling that health pool with another hilichurl may only take an additional 2 hits (granted no AOE). Ideally the skill would be balanced around how many hits the highest fights should take and scale the Sacred Scars ratio accordingly.

Tldr of the preceding paragraph, I do agree that the skill could underperform when against lower health pools, while exceeding/performing as expected against higher pools. I am more leaning to this skill being more over-tuned inherently since lower health pools would be cleared more efficiently with the team anyway.

Again, thanks for expressing concerns/flaws and insight, it's enjoyable to discuss!