This card is a really great answer to aggressive decks, and helps slower ruby-based decks stabilize
Sine Mono-Green decks generally are creature and combat-focused, this makes Craterhoof Behemoth especially terrifying, as the X values will likely be very high, allowing you to swing out with giant creatures, all that gain trample to likely take anyone, if not the entire group of players out in one combat phase
She can either serve as mana ramp, creature removal, or, if you save up for her ultimate ability, you can deal 5 damage to any target every time you cast a spell, which is bound to win you the game quickly
If you have Rhystic Study and ways to keep a lot of cards in hand, it gets significantly less good, though
Whats interesting about these cards, however, is that they seem to represent a step down in terms of Headliner card value for Magic