Woodfall Primus Green doesnt often get to destroy things other than artifacts or enchantments, making Woodfall Primus a useful answer to planeswalkers and utility lands like Cabal Coffers
Samut takes full advantage of this, granting other creatures the player controls +X/+0, where X is their current speed, as well as making non-creature spells cost X less to cast, where X is their current speed
There likely are plans for ranked Expanded eventually, but as it is, Expanded is restricted only to casual matches, and does not necessarily feature the format's entire card pool
While the initial hype for the card has certainly died down, Varina is brought up in discussions about zombie tribal decks when Wilhelt, the Rotcleaver wont do and a player doesnt want to take on Green for Sidisi, Brood Tyrant
I distinctly remember doing a double take when he suggested overload as a drawback on a spell
Sorin, Vengeful Bloodlord would be a great addition to a midrange or control deck that focuses on gaining incremental advantages through lifelink and graveyard recursion