Below are cards that see some play, but were only released in Japan. Since RS-PK is not an officially sanctioned format, legality of these cards will depend on your playgroup/TO. Japanese tournaments typically allow them. Other than PokéPark's Latias, TCG ONE does not have them implemented yet.
Thanks to Bulbapedia for card images and translations.
Victory Ring can only be used by official tournament winners.
Turn all of your Prize cards face up. You may choose any number of them and return them to your deck. If you do, shuffle your deck. Then, take the same number of cards from the top of your deck and put them face down as your Prize cards without looking at them.
Pretty much the best card for verifying your Prizes. There is a chance that you Prize the same card you shuffled in, but it's very small.
Substitutes: Here Comes Team Rocket!, Island Hermit
{C} Psywave 10×: This attack does 10 damage times the amount of Energy attached to your opponent's Active Pokémon.
{R}{W}{C} Mist Ball 50: Discard a {R} Energy and a {W} Energy attached to this Pokémon.
Psywave is its main attack, 1HKOing Exeggutor, Delcatty, and Water-type Rayquaza δ that have a lot of Energy attached to them. 70 HP lets it survive Rayquaza δ's Ozone Flare.
Substitutes: Psywave Mew. A few Pokémon have Psywave or Psychic Boom, but Mew is the only one that costs Colorless.
{C} Copy: Choose 1 of the Defending Pokémon's attacks. Copy copies that attack. This attack does nothing if this Pokémon doesn't have the Energy necessary to use that attack. (You must still do anything else required for that attack.) This Pokémon performs that attack.
Same attack as Ditto. Ilene's Mime Jr. has 10 less HP, but no Poké-Power (so it doesn't take extra damage from Cursed Stone, Rayquaza ex δ's Special Circuit, or Raichu δ's Zzzap).
Substitutes: Copy Ditto
Victory Orb can only be used by official tournament winners.
Look at 7 cards from the top of your deck. Then, rearrange the cards you see in any order you like and put them back on top of the deck.
Victory Orb can be comboed with Aipom, forming a sort-of Wishing Star where you put a card from the top 7 of your deck into your hand. The effect is a bit stronger than Wishing Star, as Victory Orb sees 7 cards (instead of 5), doesn't shuffle the deck afterward (so you can leave the 2nd best card on top as your draw for the next turn), and Aipom's Poké-Power can be used from the Bench (unlike Jirachi, who needs to be Active).
Substitutes: PokéDex HANDY909
Search your deck for Aura's Lucario (ex) and a {M} Energy card, show them to your opponent, and put them into your hand. Shuffle your deck afterward.
Played in Rayquaza δ as a toolbox target for Castaway, which can search out Metal Energy. The Aura's Lucario part is trinket text.
Substitutes: Holon Researcher