Naganadel's GX attack is amazing, even more so in Expanded paired with Dimension Valley. A single DCE that basically lets you tie up the game if you still have 4-6 Prizes left and your opponent has 1-2. You have to be losing of course for it to be effective so it's not too OP, but it can definitely be huge when played right. Poipole can also take advantage of Dimension Valley and use it's second attack for only one energy, denying your opponent a Prize if they knock it out next turn. Even in Standard though I imagine Naganadel GX will see a good amount of play, especially if Buzzwole continues to be prevalent.
Beast Energy Prism Star is also amazing. It is a bit of a bummer that it's a Prism Star, but let's be real, if it wasn't it would make Ultra Beasts broken. Imagine being able to attach two of them and a Choice Band on Buzzwole and now Jet Punching for 120 damage to the opponent's active GX. It's still a great card even being limited to one per deck though.