I will test out all the cards not already in cube and getting a 6 or higher rating except for Tragic Slip which has already had a good amount of recent cube action
One route would pair it with cards like Lier, Disciple of the Drowned and Chimil, the Inner Sun to prevent your spells from getting countered
Garnet, Princess of Alexandria A solid 2/2 for 2 with lifelink, Garnet shines it up by her interaction with Sagas by keeping them around longer and growing, working especially well with Saga creatures
Spending a measly 1 mana to blank every copy of Counterspell, Force of Will, and Fierce Guardianship in your opponents decks is one of the best exchanges you can make
Strix Serenade Not much to say here
They are calling this the rarity key, and the rare, super rare and legendary symbols will be holographic on the cards (or some kind of shiny gradient), to make it even easier to differentiate