This particular Gruul configuration blends two strategies together
Agent is a nice option to throw a spanner in the works later in the game when you have a wide board of exerted characters
This "enters or attacks" trigger is insane, because provided you have at least one nonland permanent in your graveyard, Sin is always going to bring it back, and by the time you play him in these colors it's virtually impossible that you don't have stuff to get back
Stacking up your graveyard with powerful spells, Emet can temporarily unlock your graveyard after having 14 or more cards in the pile , letting you unleash them at will so long as it's still your turn
Where the wizard becomes one of the absolutely best Rise of the Floodborn amethyst cards is when hes paired with some of the sets cards built around taking cards back into your hand, allowing him to cycle around turn after turn, adding two lore to your total with each back-and-forth