Historically, Stage 2 Pokmon (Other than Gardevoir and Charizard, who had its own acceleration mechanic) had really struggled to keep up with the game but adding a single copy of Rosa can truly make the difference in decks like Garchomp ex or Dragapult ex, allowing them to have a much stronger late game
Starlight Spectacular is one of the few eternal-legal pieces that initially stuck out to me as a possible all-star
In addition to taxing each of your opponents' spells by one mana, slowing them down significantly, Grand Arbiter Augustin IV provides you with a significant mana discount on your blue and white spells, respectively, providing an even greater cost reduction to Azorius spells
And then, for daring to touch you, you make a 1/1 flying spirit token
But I recognize that it has its faults
Presumably now the card is banned, Discover players will switch back to the MTG planeswalker Quintorius if the Discover deck survives at all