No.
You can play as characters from multiple final fantasy games (though not all) in games such as final fantasy dissidia 012: duodecim.
Cloud is not a character and does not appear in Final Fantasy VIII. Cloud appears as the main playable character in Final fantasy VII, and other brief cameo appearances in other games in Final Fantasy. Also an appearance In Kingdom hearts which is non Final Fantasy.
In most games, any of the main character (playable) character can be stoned or petrified.
Final Fantasy VII, Final Fantasy VIII and Final Fantasy IX.
PSP Final Fantasy Games:Crisis Core: Final Fantasy VIIDissidia: Final FantasyFinal Fantasy IIFinal Fantasy: Tactics
Final Fantasy X-7? no. there is Final Fantasy 10-2 which is the sequel to Final Fantasy 10 (and is the only actual sequel in all of the final fantasy games) and there is Final Fantasy 7, but there is no Final Fantasy x-7. the games may be made by the same people but do not relate to each other in anyway other then the fact they are Final Fantasy.
Between all the games and antagonists/protagonists and being a true Final Fantasy fan I'd say it would have to be Sephiroth. But of course everyone has their own opinion.
There aren't any Mario games with final fantasy characters.
Sin was only in Final Fantasy X, and mentioned in Final Fantasy X-2.
In Final fantasy IX you can set the controllers to respective characters who will then be playable by that controller in the battle screen. Controller 1 however wil always control the main character on the world map / area map. This feature also appeared in several re-issues of old Final Fantasy games for the Play Station - i.e Final Fantasy VI
There are 3 final fantasy in a playstation 2 console, Final fantasy X Final fantays X-2 And Final Fantasy 12
There is Final Fantasy XIII and Final Fantasy XI for Xbox, but no games have been announced with Kinect support.