Ah, Celesteela is very nice for Metal decks. Rocket Fall can actually do pretty decent damage considering most of the top played attackers actually have 2, or even 3+ retreat cost (and only requires a metal & DCE, which is also easy to fill with Metagross in Standard or Bronzong in Expanded), and the Lightning weakness makes it a great tech vs Fire (ie, Volcanion) decks, who also have a lot of heavy retreaters. While the other two attacks do require 4 energy, if you get Celesteela powered up right away & it survives the first hit back with it's bulky 200 HP, you just need to slap one more energy one to use them (and the GX attack revealing you Prizes before you take them is sneakily useful!). Also beings some much needed power & bulk to retreat cost decks, too!
All in all, a really cool tech for Metal, and a great attacker for RC decks.