Hehe, I actually had a few written down just for fun: some for Generations/CW/TR toys and others for characters whose toys would have no way of actually integrating the Prime Master itself. However, if we allow the use of the PotP fists we can get some crazy stuff going with Combiner Wars figures. However if you ask me, there is one figure which was clearly made for such shenanigans...
He gets to combine/mix-and-match the Power of the Primes. Fear him, for he is Overlord. These draw upon the various disparate and contradictory histories to Overlord rather than any incarnation specifically.
Vector Prime+Megatronus Prime: ChÅkon weaponry trap foes in a time loop where they are destroyed endlessly.
Vector Prime+Amalgamous Prime: Assume the form and traits of any alternate Overlord/Gigatron.
Nexus Prime+Amalgamous Prime Endlessly separate and recombine in an infinite number of possible forms.
Alpha Trion+Liege Maximo: Become the ultimate manipulator able to perfectly understand his foes and exploit them.
Micronus Prime+Alchemist Prime Transform the bodies of his minions into indestructible Ununtrium.