Dina, Essence Brewer, the commander of Witherbloom Pestilence, allows you to draw a card the first time that you sacrifice a creature each turn, and can be tapped down to sacrifice a creature in order to gain life and +1/+1 counters equal to the power of the creature you sacrificed
Best Buy is clearly feeling the party vibes
That means if you add a green mana during one step or phase, you can spend it during a later step or phase, or even a later turn
The format gives a nod to the Regional Qualifiers of old (Pro Tour Qualifiers before that), which is a strong indication of good things to come
It doesnt hit Jace, Vryns Prodigy, but we have that covered with Wild Slash and possible Fiery Impulse
Im sure this is what happens