For legendaries, I mean, it's a big reward to find one in a booster pack, so I think they should be allowed. :o As for Energies and Trainers, I can't really think of anything. There are so many Trainer cards that if you tried to do something that corresponds to that card, it'd take you forever and a day to list them all. I guess you'd just be down a Pokemon? ;( Or, in the case of Energies, consider it a "wild card" and you get to pick a Pokemon of that type. But the Trainer cards are just so varied, it's hard to come up with a standard for them.
Also, for people that don't want to buy booster packs or just can't, but have cards, perhaps shuffle a bunch of them together and draw 6? Cause I find this challenge really interesting and cool, but I don't feel like buying booster packs just for the sake of it. But then you have to take in to account how people will put in legendaries and such to shuffle in and that could be a problem. ;( I probably wouldn't...I have a ton of decks I used to battle with and could easily use those, or get my sister to select about 30 cards from my book, shuffle them, and have me draw from it.
Also, I think it'd be cool if you require certain moves. Like some cards actually have a real attack on the card for the Pokemon to use, and if you have one like that, you have to use that move/those moves? Or make it totally optional. Haha, sorry I'm like...giving you so much lol. I just really love this idea for a challenge and wish I had thought of it myself. ;P
Edit: random names for the challenge blahhh
Booster Pack Challenge
Random TCG Challenge