Appearance: Like most Wutaians, Yuffie isn't particularly tall, nor particularly broad. He's perhaps 5'6" at the most, with slim, just-this-side-of-feminine shoulders, olive skin, and dark brown hair which just barely reaches his shoulders. (In the game, Yuffie was 5'3" and shorthaired.) He inherited his mother's gray eyes and high cheekbones, and has lips that are very full for a man. Even worse for him, his hands and feet are small, and his wrists are deceptively thin. All in all, his frame is frail looking, much like the girl he could have been (which is actually kind of ironic, since original universe Yuffie looked like a twelve-year-old boy).
Unlike the original universe Yuffie, his clothing style leans toward the long and baggy. He likes cargo pants, cargo shorts, anything in khaki, and the colors green and blue. Where OU!Yuffie liked to show off her flat stomach, he prefers to show off his upper arms and lower legs with sleeveless shirts and baggy shorts.
Personality:
You'd be amazed at how cheerful Yuffie can be. It's like, I dunno, he's allergic to being serious. The only times we've ever seen Yuffie down in the dumps were immediately after Aeris died… and immediately after Shalua died. This version of Yuffie, by the way, was totally crushing on both Aeris and Shalua, and is still mad they're dead.
Yuffie's primary coping mechanism is humor. His life hasn't been easy, and in response, he flips off the world and laughs at the general absurdity of, well, life, the universe, and everything.
That doesn't make him an idiot. He's of at least average intelligence (perhaps marginally above average) and is capable of taking things seriously, though it usually requires his life or someone else's being on the line. His general response to stress is to crack a joke about it, be it snarky, lame, or genuinely funny. After that, he buckles down and does what he has to do.
He has a habit of poking fun at others. For the most part, he's just teasing, but he often doesn't know when he's crossing the line between 'funny' and 'mean.' And he doesn't stop. Every time Vincent swishes his cloak, every time Cid twangs, every time Barret is completely incomprehensible, Yuffie is there, trying to Make It Funny. And, if you don't take yourself too seriously, he just might succeed.
Another thing to consider: Yuffie isn't exactly acquisitive, but he doesn't really THINK about ownership. He can and will take anything that's not nailed or chained down, and he's been known to go after the secured stuff, too (though that's rarer). Also, finding his way into locked apartments or houses is pretty much automatic, so he has no real concept of "your house" and "my house." Privacy? "Pfft, whatever," he says.
Let me repeat that: if you are talking to Yuffie, he is very definitely looking at your stuff, and then he is taking it, and then, because his self-preservation instincts are not high, he is probably rifling through your wallet right in front of you. Shiny things? He wants them. Materia? Shit yeah, he'd tap take that. Naturally, I won't take anything without the mun's permission, but I will definitely be asking. And just as naturally, he'll give it all back if you shake him a little.
Abilities/Strengths:
His primary advantages are speed and dexterity, with a side of martial arts training. His strong point is his aim with a ranged melee weapon, usually the Great Shuriken but occasionally knives, small shuriken, lamps, Tonberrys, smoke grenades, Mudkips, lampreys, etcetera.
Let me expand on that a little: Yuffie's a fast little bugger. He is Speedy Gonzalez mixed with Speed Racer and a side order of "Holy shit that kid is fast!" The kid probably speed-reads his own thoughts. He runs rings around larger people.
Secondly, he's a trained martial artist and acrobat. We know for a fact that his OU, female counterpart was teaching martial arts to kids in Wutai around Advent Children. Also, in Advent Children, the original universe Yuffie was pulling some crazy stunts like running up walls 100 feet in the air.
Thirdly, in Dirge of Cerberus, we see the original universe Yuffie use a flashbang to temporarily stun Rosso and save Vincent's life. So she presumably knows something about explosives.
Finally, I played Yuffie as lightning-aligned, so he's equipped with a Bolt Armlet, All + Lightning, Steal, and the Leviathan Summon (the last of which may or may not work in Template. Can the gods be summoned by the ambiguously dead?).
Weaknesses:
Being fast and flexible limits muscular strength, so he isn't going to be kicking people through concrete anytime soon. Just because he can get enough momentum behind his Great Shuriken to, you know, decapitate people doesn't mean he's actually all that strong-it's a matter of swinging things around very, very quickly.
Also, he's thinner and wirier than an anorexic streetlight. He might be durable compared to non-AVALANCHE members, but he's nowhere near as indestructible as, say, Cloud or Vincent. Anybody big enough could snap him like a twig using only a patented look.
And let's not go into the weaknesses of his personality. He's impatient and selfish, quick to anger (though usually also quick to forgive). Yuffie's the first one to feel hot, cold, sweaty, or like he's got itchy trigger fingers. His impulsivity makes him unpredictable, but it's more likely to land him in trouble.