Very, very kind of you! Thanks!
Just one thing I'll put out about balance: I particularly enjoyed thinking up Diomedes' combat style (i.e. 'If Diomedes would normally create the illusion of an attack and slay his foe by taking advantage of an exposed area ... '), just because it managed itself quite naturally. Rather like, say, Gáe Bolg, it looks overpowered as anything, but there are an oddly large number of canon skills which seem to moderate its abilities. EoTM (False) allows you to react to unpredicted attacks; Diarmuid's EoTM (True) has him quickly work out how to fight an invisible sword; Instinct is very similar to EoTM (False); Magic Resistance will mitigate the effect at most levels, and cancel it outright at higher ones. Besides the incidentals, a load of skills are actually meant just to screw over people using mental interference: Bravery and Vitrification and Soul of a Martyr. Those three and MR even can hold up one of his Noble Phantasms, the 'powered-up' form of his normal fighting style as it were, which forces him to fight that bit smarter.
All that, and at the same time, it can look really cool in a description - just the idea of Diomedes convincing his opponent that the stab is coming low and then putting his spear through their chest seems like it could work really well as "what the hell is this guy doing?" moment for the protagonists. I enjoy the fact that a good application of one of his skills is enough to make competent warriors look like fools. Diomedes is good, but he makes himself look brilliant by turning the opponent into a stumbling idiot.
And better yet, when we advance it to the Noble Phantasm level, it lets me use one of the Holy Grail mechanics which Nasu tends to pass over (essentially because the Fourth and the Fifth were messed up) - that you ought to be identifying an opponent and his/her weaknesses. If you let Diomedes do that, all of a sudden he's convinced you that the poison which finally killed [you, the mighty hero X who could not be defeated in battle] coats his spear. And then you make it real for him, so he can kill you. Ultimate trolling.
Actually, re: Diomedes - do people think that a Berserker would be more or less susceptible to his style (i.e. they're consumed by rage and tend to disregard most distraction, but they're also non-rational)? My thought, partly going from what happened with Dark Berserker in HF, is that they'd be more vulnerable to convincing illusions. Instead, it's Mental Pollution that works (roughly as the canon description has it) and breaks down his illusions because he's unable to discern how his opponent might see the world. Of course, this is not to say that Berserkers might not have Mental Pollution ...
(Oooh, wow. That turned into wordswordswords.)
And I would comment on yours in return but ...
Sorry.I feel bad, again, skipping over so many following profiles but- I haven't seen/read/played any of the media involved, so I can't accurately judge how well they're set up.
(I can fulfil a request for some Servant or NP, if you'd like. I do feel bad about getting that sort of praise and not giving anything back).