A new card type, inspired by Final Fantasy summons like Shiva, enters the game with a lore counter, gives an instant effect, and stays for a few turns before vanishing, copying the short but strong nature of summons
As a control colour green doesn't have much disruption nor does it have much card advantage both of which are important in a control strategy
No other box toppers were shown in the most recent stream, but more variations on existing Magic cards were
(You may cast cards with retrace from your graveyard by discarding a land card in addition to paying their other costs.) If a spell you cast with retrace is countered, it's put back into your graveyard
You can sacrifice a good number of lands and then search for Field of the Dead as part of its effect
It takes a concept (a species in danger of vanishing from the earth) and melds its mechanics to fit that idea (the creature literally has vanishing, but you can stop it if you take the right actions)