With the cards in this booster's lineup, you'll be able to strengthen previous decks based on the various protagonists as well as [ST-20] and [ST-21]
20 Monsters, 10 Spells, and 10 Traps isn't a good idea more often than not, so replace the Imperial Iron Walls with 3 Upstart Goblins
5 Treasures Gruul is one of the best color combinations at making Treasures, making it a powerful archetype within the color combination
Im not inclined to pay cash, yet, but I feel like if you can out a Standard card thats like $4 and bound to go down for a set of these, these can retain value better and if they really go up quickly, you quadruple your gains because you have four times the exposure to upside
Because it's a variant of split second, players also can't cast spells or activate abilities while Slaying Mantis is on the stack