One of the largest (or, rather, tallest I suppose) Beast Machines toy ever released is the Supreme edition of Cheetor. His mechanical cheetah mode is about the size of an actual cat. His spindly robot mode is nearly a foot tall. He's loaded with play features both electronic and articulated. He was available in 2000; in Japan, he came out in 2004.
The combined form of the Universe Micromaster Aerialbots is Superion, an amalgamation of six robots plus their pack-in accessories that serve as connectors, head, and extremities of the gestalt warrior. While in Japan, the original source of the design ( Sixwing , 1992) was available in a collected set, this combiner needed to be purchased one bot at a time in the 2007 Universe release.