Magic: The Gathering has dabbled in dark, demonic material from the very beginning of its existence with Alpha, the card games first set, which released in 1993
What affects the value of Stolen Vitality
Not just that, but if the card is sent from the Field to the Graveyard while face-up, it can destroy any card on the Field without Targeting, which is one of the best forms of removal
Cards that are in great condition (i.e., little to no visible damage or wear) tend to be more valuable, too
Deeper in blue is Mythos of Illuna, but there arent great targets up the curve for it, and sadly you cant copy enchantment tokens with Battle and really go off