Overall) - Ob Nixilis Reignited with a Shoutout to Vraska, Betrayal's Sting Everyone's favorite Commander Classic planeswalkers
As for Pioneer, multicolor Greasefang, Okiba Boss shells sometimes play Mana Confluence already
Ariel Singing Mermaid comes to mind thanks to her Singer 7 ability allowing her to sing high-cost Songs and contribute a large chunk of the new Sing Together mechanic
While resolving Papalymo Totolymo's second ability, the next opponent in turn order who lost life this turn chooses a creature with the greatest power among creatures they control, then each other opponent who lost life this turn in turn order does the same
Big Mother Mouser | 4 Colorless Mana Artifact Creature Robot This creature enters with two +1/+1 counters on it
It's also a good resource for figuring out how much your cards are worth once the new set is out, so if you pull any Surge Foil cards in your booster pack preorders, you might suddenly find yourself with quite the nest egg