Hmm... Looks interesting, I'll put one in then.
Mechatril (real name unknown), participant of the 6th Grail War
Distinguishing Factors: Late teens/early twenties. Black hair. Wears glasses. Usually walks around with a book in hand. Wears long scholarly mage robes whenever possible
Notable Abilities: High theoretical knowledge. Familiar with many branches of magic and is capable of practicing most of them, in controlled situations. Favors using various ritualistic spells and setting magical traps, both of which takes a high amount of time to prepare. Has a number of spell books for quick casting, in which pre-prepared spells are stored in the pages through magical ink and ritualistic bindings. Low physical capabilities, but has started brushing up on reinforcement magic for his limbs, in the hopes of boosting his frail scholarly legs in "tactical retreats".
Notable Relationships: Knowns many figures in the Magus Association. Was acquainted with Sion Eltnam Atlasia before her encounter with Wallachia. Studied briefly under Lord El-Melloi II/Waver Velvet.
Reason for Participation: Accidentally entered the sixth war due to a monumental screw up in a summoning ritual for a spirit guardian, which instead landed him with a Servant and command seals. Unfortunately, the servant he summoned, Assassin, is very determined to win the Holy Grail war, and so has threatened to kill Mechatrill should he try to back out of the war. Thus, deciding that trying to get Assassin killed is far too risky (and being far to curious for his own good to simply let the Holy Grail go just like that), supports Assassin wholeheartedly in the Sixth Holy Grail War.
Notable Quotes:
"I'm a scholar, not a warrior, just who do you think I am, Emiya Shirou?" - When Assassin commented on his reluctance to face direct combat
"You know, I am this close to using a command seal to order you to off yourself" - To Assassin on a really bad day
Servant: Assassin - To be added
I do need a bit of help thinking of a good assassin through, as I'm not very familiar with all the requirements for a servant to be a certain class. I guess some other servant is fine too, except caster and berserker.