I think it's kinda like the album, where for the most part each rapper wrote their own verses. Mike said he wrote all of his verses and the singing parts on the album, I'm assuming that goes for the mixtape too.
every rapper wrote their own part; mike wrote all the singing parts, both on the mixtape and on "the rising tied". mind you, half the songs on the mixtape aren't actually fort minor songs; i only realised this recently as i read the tracklist on the cover for the first time in ages. ha. - "bloc party", "all night", "S.C.O.M.", and a few others, i think, are not under fort minor; they're just collaborations. "respect 4 grandma", "cover and duck", "100 degrees" and others ... those are fort minor. just thought i'd point all that out because it was a big deal to me.
well, i've heard "sweet child o' mine", of course. but what i was saying is that, if you read the tracklist off the mixtape cover carefully, you'll see that not every track is labelled under fort minor, despite being on the fort minor mixtape.