By releasing starter decks as each new set comes out, even longtime players are introduced to new strategies that they may not have thought of previously
You have one of each basic land that can be fetched by specific cards
Turntimber Symbiosis comes into play untapped when needed, further lowering its opportunity cost, and since green decks tend to have big finishers like Craterhoof Behemoth, being able to dig seven cards deep in your deck to find them is quite powerful
Its a perfect fit for go-wide landfall strategies
However, its in Arthurs ability that he truly shines: when played, he can give a chosen character Challenger +2 and Resist +2 (that means they get +2 Strength while Challenging and a reduction of 2 damage thats being dealt to them), plus they can also challenge Ready, not Exerted, characters on the same turn too