As of their debut in March of the Machine, there is only one subtype of battle card, known as a Siege
You cast Baral, Chief of Compliance on turn 2
Then, for its final two chapters, the next creature spell you play gains haste which can provide some stunning surprise attacks and delivers yet more ammo for mono-red strategies (or Jeskai Prowess strategies) to run roughshod over Standard for the foreseeable future
If this card somehow enters the battlefield with its back face up, it didn't transform, so you won't choose an opponent
But here's the thing about Gluttonous Hellkite: even if you cast it without paying for X, it's still a 3/3 flying trample dragon for three mana
Each version is mechanically identical to the main set version, which can also be found with extended art in Bundles, Gift Bundles, and Collector Boosters