Since Eminem's come back, he has yet to get on a track with one of the lyrical juggernauts.
Lyrical Juggernauts (in no order):
Tech N9ne
Soul Khan
Wax
Immortal Technique
Hopsin
Diabolic
Dirtbag Dan
(leaving out Kid Twist since he's only a battle MC, but he should make music

maybe 3 or 4 more that i can't remember off the top of my head
Anyway, Tech N9ne is the most known artist out of all of the above and Tech N9ne has tried to get to him on multiple occasions.
If he wants to do this fast rapping shit, get on Worldwide Choppers, y'know?
He pushed back his verse on So Lonely so that he could work on The Reunion? FUCK is that shit?
As much as I love Eminem and what he has done for hiphop music, I can't stand him right now. He's fucking Eminem, he has the ability and the opportunity to collab with anybody at any time. And don't tell me Em doesn't know that rappers of this caliber exist. He's been spending a lot of time with Royce, who I can assure you is aware of these artists.
"I got fans like Royce da 5'9, you got friends like Troy the white guy"
-Soul Khan vs. Sensa
He tells Tech N9ne that he's gonna need a month to do So Lonely (knowing that Tech doesn't have that kind of time), and then he says in these interviews that the Bad Meets Evil idea didn't even come into play and most of the songs were recorded on the spot. Fucking Royce didn't even give enough of a shit to fix his opening verse of I'm On Everything!
