The FunPub version was 5 guys from seemingly random parts of the multiverse fused into one: Skyfall, Landquake, Topspin, Breakaway (specifically not Getaway), and Heatwave. According to the Covenant, he's basically an ever shifting mass of parts that he can divide into multiple autonomous bots as needed. But, in the aligned fiction he and Megatronus have a past when it comes to being rivals for the affections of Solus Prime...who Megatronus eventually killed. So if I had my druthers, the two boxed sets would be Megatronus and Nexus. The storyline being Megatronus obtaining the Enigma after a battle with Nexus, and infecting it as we saw at the end of the TR Machinima. This gives Megatronus the ability to fuse 5 loyal Decepticons (from whatever figures happen to be handy) into a new body for himself. Nexus counters by fusing 5 Autobots using his own essence. This justifies the boxed sets replacing the pack-in Enigma with their respective Primemaster.