A Freestyle Rap can be made up of Lyrics that U wrote but yet, they are not to be fitted for any song you're doing. you jus have alot of hot Rhymes in there of sum shit u jus wanted to say and however U really wanted to say it..
and then u have Freestyle Rapping or just regular Freestyling where u jus go in an do this shit off the top of your head.
Common, KRS-ONE, Eyedea, Mos Def, MC Juice, Supernatural, and Sage Francis all Freestyle off the top of their heads..
While Murda Mook, T-Rex, Loaded Lux, Math Hoffa, Goodz, Arsenol, Reed Dollaz, and Cysserro, they all Write their shit down, but its not really fit for a song. they just random hot punchlines they can use in battles or whatever. so they good at making Freestyle Raps on sum random shit.
To improvise rapping sentences without recycling the stuff that you've wrote on a piece of paper. Rap and Freestyle Rap are two different things.
Jin can Freestyle Rap pretty good, but Loaded Lux be writing his stuff.