That's decided for you, and you won't know who you have until you bust open the box
GX did a lot of things as far as reshaping the franchise's competitive metagame
Also as its name implies, Phantasmal Flames will have a special focus on Fire- and Darkness-type Pokmon
The field spell is designed to recover the traps which I expect would get used a lot, and give me some breathing room if one of my Lethal Lords is killed and I'd normally be wide open for attack
And thus, Emerald Charm was a handy solution to any global enchantments (for you younglings, those enchantments which don't enchant anything in particular, such as Form of the Dragon or Worship), a way to bring flyers down to earth, and a second use of a utility creature, all wrapped into one neat little charm