For the most part, however, playtest card effects tend to stay as playtest cards
That means cards that help you search your other cards (Ultra Ball, Nest Ball, Battle VIP Pass) and the ones that let you draw, like Professor Research or Iono
Midnight Hunt's Red Cards Two red cards in Innistrad: Midnight Hunt are highly valuable, starting with Moonveil Regent , a 4/4 Dragon that can discard and draw many cards with ease to refresh the hand, then deal damage to any target when it dies
Go after more vulnerable Pokmon with Iron Hands ex and its Amp You Very Much attack, which does 120 damage and lets you take an additional Prize Card when taking a knockout
WotC has even rested the concept, releasing recent major sets with no serialized cards to let the market breathe.