Looking back, it’s already been four years since XXL inaugurated its Freshman class series. Since its debut, dubbed “Leaders of the New School” at the time, the annual issue has become a coveted platform for upstart MCs to take their careers to the next level. Some have inevitably fumbled on the opportunity, while others have been able to use the XXL cosign to the fullest.  XXL Freshmen have always operated like frat brothers. It's not unusual to see spitters from different classes join forces on the mic. Earlier this week, Kendrick Lamar, of this year's class, released "Hiii Power" produced by J. Cole, a Freshman from last year's class. XXLMag.com takes a look at the collaborative works created between our Freshman alumnus. Which one is the hottest?— Kai Acevedo and Ralph Bristout