While a 1/1 might not be much to write home about, as soon as you get ten permanents in play and you get the City's Blessing, all your Saproling creatures get +2/+2 and suddenly become 3/3 threats
Since his release in 2019, he has been one of the most ubiquitous Black cards in the format, showing up in practically every deck that cares about sacrificing Creatures, reanimating Creatures, discarding Creatures or forcing opponents to discard Creatures, or Milling Creatures, which is about 90% of Black decks
Thassa also works great with cards that have enter the battlefield triggers or might have other effects on them that might be preventing you from attacking or activating abilities
Japanese cards often release months before English ones, and SARs especially tend to hold value due to lower print runs and premium print quality
Summary Build a powerful energy-themed deck with legendary creatures like Rex, Cyber-Hound, Atraxa, and Liberty Prime, for game-winning combos