Originally Posted by egghead
What's the story on why he's so big? And does he get smaller later or they just wanted to make a set with Vector Prime?
Starscream absorbs some of the power the cyber planet keys hold ... thus, the gigantic growth. When the keys are all together, it revives the spark of Primus ... aka, the good unicron.
By taking in some of the spark, Starscream gets to near planet size.