Prerelease Kit info:
Wash Rotom Group:
x2 Piplup (60HP)
x1 Piplup (70 HP)
x2 Prinplup
x2 Empoleon
x1 Shaymin (Sky)
Lucario Group:
x2 Gible (Ascension)
x2 Gabite
x2 Garchomp
x1 Riolu
x1 Cynthia
Heatran Group:
x1 Magnemite
x1 Magnemite
x2 Magneton
x2 Magnezone
x1 Heatran
x1 Looker
Gumshoos Group:
x2 Electabuzz
x2 Electivire
x2 Yungoos
x1 Gumshoos
x1 Volkner
2-3 Supporters and 2-3 Item cards included, same ones as in previous set's prerelease kits but with the addition of Pokemon Fan Club. Spiritomb may also randomly appear and will replace one of these Trainer cards.
My 2 cents:
So both theme deck mascots are featured here. Guess it wasn't too surprising that Lucario would feature both Garchomp and Cynthia, I'm sure it'll be like this in the theme deck as well.
About Spiritomb; it would be good if you do get this in your kit (if not maybe you could still pull it from a pack - it's only uncommon). It can shut down anyone who tries to build a deck based on soloing with their basic GX Pokemon they were lucky enough to pull, and it can be especially good for the Lucario Group as you can use it to retrieve back your Cynthia (ironically Spiritomb is another one of Cynthia's Pokemon lol).
Playability wise for the prerelease; I think the Wash Rotom Group and Lucario Group will be the ones you'd want. Lucario would definitely be the ideal promo if you do get his group since no Lucario is included otherwise (unless you get lucky with your pulls). You'll probably want the Gumshoos group as your other group as having two different Stage 2 lines might be a little too clunky to build a prerelease deck on. Gumshoos is also fairly solid and can fit in easily being colorless.
From a collector's perspective, you'll definitely want to get the Heatran group. Both Magnezone and Heatran are holos in this set, so here we have 2 exclusive non-holo versions. No other group has any special non-holo cards. This group may also be pretty decent playability wise at the prerelease as well (it'd definitely be good if you're lucky enough to pull a Dusk Mane Necrozma GX), but you'd need to watch out for those Electivires from the Gumshoos group. Hopefully you pull a few Escape Boards so you don't get stuck in a paralysis lock.