The Giant Purple Griffin was one of the original Megatron's most awesomely ridiculous creations: a giant flying building shaped like a Griffin. It was supposed to do... something. The Giant Purple Griffin had a mane of prehensiletentacles that could be used to grasp at opponents.
It is unclear exactly what Megatron planned to do with the Giant Purple Griffin (aside from the obvious "conquest"), as it was destroyed by the Aerialbots before he was able to put it to good use. Aerial Assault
Note:The name, "Giant Purple Griffin", is fan-created, as neither Megatron nor any other character ever referred to the device with a proper name, calling it simply "the fortress" or "the griffin". Many fans also refer to it as the Big Blue Griffin, 'cuz, hey, alliteration.