[@vancexentan] 
For Guile and Subterfuge I looked at Chevalier d'Eon as a basis of what Assassin could do and decided to improve on it as compensation for the lack of combat capabilities. Along side the fact that it is Assassin specialty in acting such an area, I thought it would be fine giving base-line [ B Rank ] in that skill to him that could improve originally.

If that is not fine, then I am okay with making it at maximum be [ B Rank ] and become another skill that has a different rank within combat that suffers a decrease in rank to [ C Rank ] until he studies them. Allowing the skill to be raised back to its original value since he is intended to be more of a socialite along with the fact its based off on [ Human Observation ]. Making this skill rank to be a maximum of [ B- ] situationally and knock off the parameter decrease. Thoughts?

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[hider=Noble Phantasm Lore / Mechanics]
Lore wise, Assassin's Noble Phantasm is only seen as a killing technique and this view point is also supported by himself as well, being 'an entity made for killing' at one of its simplest functions. Allowing him to harm others not physically but on the spiritual level that prevents mundane protections from keeping them safe. That is all that matters for the other Hassans and Assassin himself.

In more depth, this Noble Phantasm works on information since it goes through the Soul/Records of an entity first and manipulates it, the changes written on the soul will then try to manifest and overwrite the present with the new variables recorded. An example would be using this Noble Phantasm to inflict a wound on a person, even though the weapon didn't pierce their body, by changing what is recorded in the soul is then reflected outside the body. The same can be said about healing as it restores a person to a previous state recorded within their soul as all the memories that have taken place are there, wounds can be overwritten within the soul that would be reflected on their body as they are 'healed'. My idea that if a person is less human, the nature of their soul would be more difficult for Assassin to handle due to its foreign nature plus the fact that it would inherently be stronger and more resistant to change than a human soul. 

To erase someone memory with this Noble Phantasm is possible as it gets rid of it from the source, resulting in varying degrees of amnesia if a person cannot defend against it that could change them depending on how long Assassin dedicates himself to. However, to remove or change the foundation that someone is built on and has already happened is near impossible as they are variables that are more concrete and solidified beyond the grasps of manipulating as a principal to nature and would require much more power to budge them (like a wish from Holy Grail to accomplish, very High-level Thaumaturgy, or Magic to name a few). To do such a thing, the actions that proved their existence in the world would effectively have to be erased or changed before the soul twists the body to that degree which is beyond the capabilities of this Noble Phantasm. Think Grand Order when trying to erase the existence of something, as you must prevent the result from happening in the first place to cause disorder to the rest and pervert them or outright destroy them. These critical events can be reinforced however to prevent change in a being's existence or up to a point that even boost their abilities if Assassin should desire as it empowers their physical existence and standing to make a change to the world once again.

To sum it up, this Noble Phantasm works in the present and cannot change the far past. It can heal people as well as harm others and a whole lot of things if Assassin puts his mind into. His limitations are the predefined rules along with the general sense that Assassin cannot extend this ability effect to anything outside the area of the bodies of himself and the targets that he has in mind.  [/hider]

[Hider=Noble Phantasm Defenses]
Moving on from that, this Noble Phantasm is only at its fullest potential against straight boring humans as they hold little weight in this world but even then there is a limit to what Assassin can do to them.

Resistances to this technique begin to build up so long as they have 'Mystery' and 'Presence' to them, which all Servants above the existence of wraiths should have a fair amount and results in a base amount of defense against this technique. When stacked up with Class and Personal skills plus the lore of other Heroes, they simply gain more defenses the older they are and how prominent they are.

Saber has [ A+ Magic Resistance] that prevents this skill from effecting in any massive way even if Assassin were to approach her via touch. The same with Lancer being blessed by the blood of Christ which would suffice in enough mystery to again prevent major changes added on top of his own [ Magic Resistance ]. Rider would have some resistance from his existence tying him closer to being an elemental spirit which would provide another layer of defense compared to other servants. Archer being the most mundane would preferably keep to being at range and use that bow of theirs to what Archers do best but resistances again from [ Magic Resistance] and what fame that poem has ontop of it. Berserker has dragon blood in her, she's practically immune to the serious effects of this Noble Phantasm even if its not stated on the Sheet with the [ Magic Resistance ] built into it and besides why would he want to get rid of his karaoke buddy? Assassin against Caster would be a chess game of one piece that he has and Caster having several other pieces to defend himself as king but that sword is whole different topic of hurt. 

If you look hard enough, this Noble Phantasm is only dangerous against those who didn't deal with the supernatural world and those who are heroic spirits that have recently came into fruition. Even then, these Servant's best defense are the accumulation of their stories which is their Noble Phantasm that can provide solid defense as it is a representation of who they are in the present if there is significant connection between the two. Only Servants who are either low-tier of the spectrum or their existence being considered a wraith is capable of being significantly affected simply due to them not have enough 'presence' to solidify themselves to the world. It is similar to Nobunaga Oda's Noble Phantasm flipped around as it excels against normal people but is abysmal against those who have left a significant influence on the world or vice versa (the world having a significant influence on those Assassin is trying to effect).

So yes, he is perfect against Masters and the occasional Servant who are in the same tier-level as he is but outside of that there is nothing much he can do. In the end, like any other Grail War is to hide your Master against Assassin and you'll be fine!
[/hider]

Hopefully thats a good enough explanation, it took me some brain storming to spit out English rather than Nasu-talk. If this doesn't suffice then I can make it more concise and take out the fluff, so just tell me if you need it ^^ Sorry if everything is a bit confusing, Fate series does that to me!