An American writer goes to a remote Welsh manor on a $20,000 bet: can he write a classic novel like "Wuthering Heights" in twenty-four hours? Upon his arrival, however, the writer discovers that the manor, thought empty, actually has several, rather odd, inhabitants. House of the Long Shadow
Vincent has rolls in most of the spin-offs that have to do with Final Fantasy VII. This allows him to meet a wide variety of characters within the world. The only ones I'll cover are the ones I've actually experienced. As such, this will cover his cameo, minor, or supporting roles in Crisis Core, Final Fantasy VII, and Advent Children.
Crisis Core
Vincent has a very small role in Crisis Core. When Zack travels to Nibelheim with Cloud and Sephiroth, a little boy gives Zack something to do. Zack takes the tour of Nibelheim through the "Seven Wonders of Nibelheim" Quest. The fifth spooky quest is maked by blood curdling moans coming from the mansion. Zack can visit the Shinra Mansion basement and go into the coffin room. Vincent is the fifth wonder of Nibelheim, sleeping (apparently not so peacefully). Although Zack can open the coffin, the player never sees Vincent - but who else is sleeping down there?
Final Fantasy VII
Vincent appears as an optional character. You don't have to get him, which saddens me (and yes, that is mostly Vincent-bias). He holds information about Sephiroth's birth parents and the Jenova Experiment. He states flat out that Lucrecia is Sephiroth's mother but does not deny that Jenova is also Sephiroth's mother due to an experiment. However, he insists that the woman who gave birth to Sephiroth was not Jenova but Lucrecia. Ultimately he joines Cloud's group because he wants to atone for his sins and get revenge on Hojo. He has a few lines throughout the game, but it can be played without him. He also has no cut scenes. He tends to stick to himself and brood, though you can see him comment on specific things. He will comment on Don Corneo's stupidity if you got to Wutai with Yuffie. When Cid is made party leader, Vincent will also comment that he wishes he had Cid's "go get 'em" attitude. When he confronts Hojo for the final time, he tells Hojo that it was him that should have slept to atone, rather than himself. I take this as Vincent realized that Hojo made the mistakes, but that it still weighed on Vincent quite a bit. I get the idea that later it came from the notion that he hadn't stopped Hojo sooner.
Advent Children
Vincent appears as a supporting cast member in Advent Children. He saves Tseng, Elena, and Cloud from the Silver-haired trio. He also helps Marlene convince Cloud that he doesn't have to fight alone. Vincent has knowledge of Geostigma and the Silver-haired trio, recognizing that they are the pupa of Sephiroth before many of the others (perhaps even Cloud himself). Vincent always has extra insight into what seems to be going on. He has more screen time than in the original game. His purpose is that of someone giving knowledge as he tells the others to let Cloud fight alone. He understands that Cloud is looking for something particular and he knows that Cloud will find it again. He's actually quite supportive of Cloud. He trusts in Cloud to handle the party going so far as to call him and have him tell Yuffie that she has no right to call his phone. I doubt Yuffie would listen to Vincent, I also believe that this is the impression Vincent has of her. So he calls party leader to get the nonsense to stop. For all his knowledge, he's still not very adept at talking to people. It also makes him seem like a cranky and fickle man.