Some background on this Megatron:
This robot here never appeared in the RID cartoon, of course, but rather in its direct predecessor among the Transformers franchise: Beast Machines. This series saw Megatron change himself into a giant floating head as he prepared to fuse his consciousness with the sparks of the entire Cybertronian race. Unfortunately (or maybe fortunately) Beast Machines ended quickly and this toy never made it to the shelves. Until it was resurrected for RID.
(source: TF Universe)
Head Mode in cartoon: http://www.youtube.com/watch?v=WV39DirA5rQ