Yeah, I'd been figuring that the head would remain pretty much intact in the form change, and thus it'd still retain access to the the breath weapon we'd presumably give it.
I was thinking that the initial form would probably be slower but more maneuverable, owing to the armor and wings, respectively. Once it initiates the form change, it'd be faster because it was lighter but less able to turn and stuff. So, like, the first form would be the kind to hover on one area of the screen, move to a different spot occasionally, and make more precisely aimed attacks, while the second phase would be the type to zip across the screen in a straight line, maybe leaving leaving a trail of something to cause damage, not staying still nearly as much, to try and present how I was visualizing it via videogame mechanics.
To probably be more specific than is necessary, I was thinking it'd lose the entirety of its wings, alongside torso armor and some armor on the limbs, making its torso more of a tube and its limbs thinner and stubbier in the transformation. The second form would then probably fly via magnets or whatever other super-science option we have.