The UI has been modernized and the game rules engine was built from the ground up and is written in a way that allows for endless development
Green Slime, on the other hand, is a way to not only get rid of powerful pieces like Rhystic Study or Smothering Tithe, but also stop them triggering at all
As soon as it enters the battlefield, a player gains two rad counters, setting the tone for the mutation that follows
Beginner-Friendly Formats Constructed Formats Standard and Brawl are Constructed formats, meaning that players bring their own decks to events, as opposed to building them as part of the event
The mana could also go towards land destruction spells such as Acidic Slime, Reap and Sow, and Woodfall Primus, to prevent control decks from stopping Thrun with Iona, Shield of Emeria
That said, not exactly in the center of what I would define as the -1/-1 counters design space