What makes it really powerful is the fact that it has convoke, which allows the caster to tap creatures to help them make the casting cost, with each creature tapped being worth one mana
You may play one during each of your turns for free
As you pointed out, the difference between Pokmon EX and Pokmon GX is that the former ones are always Basic whereas the latter ones are always the stage they are supposed to be [1] (except for Tag Team GX cards which are also always Basic)
Yes, our modular design allows for safe, secure stacking
Stitch, Rock Star Stitch, Rock Star D23 Expo promo
This means that your opponent could then cast Flusterstorm and copy it 10 times, leaving them with an additional copy of the spell to direct wherever