HR cards appear ~10% of the time, and UR cards also ~10%
However, Poisonous uses the stack, and as a result, can be countered by anything that would counter abilities, like Stifle or Disallow
We may also see this card acquirable in-person at the World Championships and PokmonXP in San Francisco, and at the Pokmon Center online with a special code, like the 2025 World Championships Pikachu promo card
Sure, it might not be the best card ever, but it will be the silver lining Adrian Sullivan needed after the new rules changes
Both are viable strategies, however, and which one you choose to run with will largely depend on the type of decks you like to play
On the plus side, it also lets you proliferate: an effect that can be worth a few mana in itself depending on the board state