Accent (or other vocal quirks; who are they voiced by?):
Shunsuke Kazama, the Yami no Yuugi variation. In terms of quirks, his voice gets pretty gravely when he's ticked, and he always has a deep edge that makes it naturally authoritative. What I like to call the “Christopher Lee Effect”.
Build (Fat, skinny, short, tall, muscular, etc):
He's a skinny, extremely short fellow, as all his doubles. But he more than makes up with it by posture and confidence - as someone once said, he looks taller. He also has some slim muscling on his arms (according to bunkoban covers) that may or may not be carried over from Yuugi. The Puzzle grants an instant workout?
Colors (Either their favorites, or the ones they seem otherwise associated with):
He shares the liking to black and purple with his former master, though with a particular emphasis on the black.
Diet (and any allergies or religious / personal restrictions):
He's a ghost.
Education:
His iffy memories don't lend much on his childhood tutoring, but he's got some sub-par academic knowledge from Yuugi.
Family (Blood and otherwise):
In terms of his late blood family, he has little to go on. Yahtzee went through the memory arc, but he only earned back the memories the Puzzle deemed pertinent (i.e. what we actively see him remembering). As such, he has a good sense and respect of his father, a kinship with his cousin Set, and awareness of his uncle. He has near-zilch knowledge of his mother, and couldn't even say if he ever had siblings. To him, his family now is Yuugi, Sugoroku, and his circle of friends.
Goods (Important things they own, or their overall material wealth):
Yahtzee has his Puzzle and deck (including God Cards), and that's all he really needs. Anything else is something borrowed over from Yuugi.
Hobbies:
He's the King of Games, what do you think? Although, he's spent a fair time in the DR exploring history and philosophy books in the library, since the former helps his understanding of what he's missed, and the later is helping him prepare for accepting his coming loss and death. Along with just being interesting.
Ignorance (Things they are particularly ignorant of or bad at doing):
He'd be horrible at domestic things, so it's lucky he doesn't have to see to that.
Job (Past, current, future):
He was the ruler of a nation, and then the eventual guardian and servant of Mutou Yuugi. Before becoming effectively friend and partner.
Knowledge (What they've taught themselves or learned outside formal education):
He's still surprisingly ignorant of life in Ancient Egypt, but he sometimes has a sense of what would or wouldn't happen then, even if he can't remember why. (Ex: Knowing Bloom's navel piercing is insulting. Somehow.) He can also read hieroglyphics, and even speak late Egyptian.
Love interests (Past, current, future):
Anzu might qualify, though it was largely one-sided on her part. He himself was more interested in his own master, though whether it's actually romantic or just a soft spot? Even he couldn't say - He's mastered ignoring the issue too much for his own good.
Music (What's on the character's ipod?):
He doesn't bother with it.
Needs (Things they need to function normally):
Peace of mind. It is hard to get here, though.
Orientation (Sexual/romantic; where do they fall on the Kinsey scale?):
Yahtzee honestly has a low attraction either way, but there's a slight leaning towards boys.
Phobias (And nightmares, traumas, etc):
His biggest fear, whether it shows or not, is actually the Puzzle itself (or his Puzzled soul room if you will). Getting locked back inside is a real fear, and it's only worse now that he's gotten used to having the freedom of his own physical form outside of it. Aside from that, he's not fond of fire.
Quarrels (Their rivals or things they struggle against):
He's had more than his share of enemies in the past, but at the moment the only rival he has is Yuugi himself. Sort of. If you count “fighting him in a duel to decide whether he dies or not.” His only active enemies now are DR people that have a bone to pick with him, not the other way around. Blue. White. Bloom. You still planning his death, little Brunch?
Religion (or philosophy and superstition in general):
He doesn't have a lot of active knowledge on his own religion or how things work, but fate is there, destiny is there, and he will meet his head on.
Scars (and other markings):
None.
Talents:
Games. Spirit summoning. Penalty games Wish gambles. Bluffing. Thinking ahead and strategy. Staying hidden (usually).
Unconsciousness (The things even they don't realize they do):
Softens up around Yuugis, lets his eye show up and glow when angry.
Vices and Villainy:
His villainous traits - namely being manipulative and merciless with opponents - have been largely curbed over the years, but they sometimes surge back when angered or the DR is dragging it. He'll also sometimes show vices people want him to (see weaknesses).
Weaknesses (Things they always give into, or things that they are really bad at):
His biggest problem is even if he is strong-willed and now free, his basic djinn makeup makes him sense other's wishes and what they want from him. This makes him want to offer them that wish, even if they'd get punished if they lost, and/or give what they want. Example: if somebody really wants him to fight them, Yahtzee will get the urge to fight.
XXX (Their overall 'rating' as a character, their level of sexual experience):
Given historical accuracy, Yahtzee probably was married, likely to more than one wife, as an older prince (debatable, depending on what his father wanted). But if he was he doesn't remember it, and his knowledge of sex comes from Yuugi's fascination of the subject. He himself has a low interest in the topic most the time. It's just not an urge that comes up a lot without a true body. He has now had a little direct experience, but in the wrong gender with the wrong person. Getting punched right after does not help.
Yearnings (Their goals, wishes, desires):
He wants to want to move on to the afterlife. He's assuming the hanging reluctance is from fear of passing over rather than a want to stay.
Zoo (Their favorite creatures, any pets they have, any creatures in their life):
Never had any, unless you count Kuriboh. It doesn't show up around others a lot, but that spirit does have a particular liking for him, and will follow him or come out if he's alone.