The most common line of play will probably be to play her and draw a card for her first trigger, then transform her the following turn before she attacks
#10 -- Deoxys VMAX (GG45) Deoxys VMAX from the Galarian Gallery is one of those cards that absolutely pops in person
Similarly, Den Protector loves to have extra options find its way to the graveyard throughout the game
Is it one of the key cards in a format, and, if so, is it a four-of in most decks
Flashback will probably still be the most dominant way to take advantage of Sevinne, with a much greater saturation of cards with the mechanic (plus cards that favorably interact with flashback, like Burning Vengeance or Secrets of the Dead)
I snagged The Abyss in pack two, which notably does not affect artifact creatures, and in the third pack I actually took Tinker over Mox Emerald because Tinker was more likely to lead to a broken start in my deck at that point, and had significantly more value later in the game