It can be anythingpower, toughness, something in rules text, the name of a card (Four Wishes, anyone?), collector number, and so on
The three-cost instant can Murder something
This makes it a decent combat trick from the hand, and potentially even from the graveyard thanks to Flashback
Instead, Id be much more excited to start with red-black, which offers premium removal and a powerful void synergy
Each booster also includes plenty of Dominaria United cards, five non-foil basic lands, two traditional foil basic lands, one non-foil full art stained-glass basic land, a random Dominaria United rare or mythic rare, and one of the five rare cards designed for the Jumpstart set
Mox Sapphire + Mox Emerald + Mox Jet For the same reasons as the original dual lands, Mox Sapphire, Mox Emerald and Mox Jet wind up as the most expensive of the Moxes