44. Busta Rhymes feat. Eminem, "Calm Down" (2014)
"It started off from just doing a dope, high energy hip-hop record into us respectfully competing and damn near battling each other,” Busta Rhymes told Complex about this flashy feat of technical abilities that took seven months. He says Eminem initially responded with a 42-bar verse, so he returned with 50 and the ante kept being raised – 60, 62, 64 – until it ended up as a tune where each rapper goes for about 2 minutes and 30 seconds apiece. "My hat is off to Eminem because he genuinely still cares about the music," said Busta. "He very much cares about being a thoroughbred MC and wouldn’t ever be the type of artist that has to worry about letting me down or compromising his skill set because he’s trying to do something that people think is cool."