If you want to perform a character action that requires exerting the card (questing, challenging, and certain abilities), that card must have been in play since the start of the turn
But if they don't, you've got plenty of ways to sacrifice your own vampires, providing you with a ready army of 4/3 vampire demons
Play boosters simplify and satisfy the vast majority of what players want in opening packs
Hildibrand's adventure fits the requirement, and being an instant means it gets you closer to triggering Y'shtola on other players' turns (Y'shtola triggers on everyone's end step)
I play these cards instead of Go for the Throat sometimes but usually along side it
Koma offers something different compared to other Simic Legendaries as it cares about interacting in combat, rather than unloading your hand with lands to draw more cards