The Jumpstart set was famous for this, creating valuable dual lands where a basic land was double printed with another card
And since elf decks are packed with cheap mana-producers, your board fills out quickly, meaning that game-ending drain can come online sooner than your opponents expect
That means you get Final Fantasy: Garland at The Chaos Shrine, Final Fantasy VIII: Children of Fate, Final Fantasy IX: The Siege of Alexandria, and Final Fantasy XV: Camp Comrades
Punish the Enemy: Expensive since it generally wont kill creatures that cost more than it, but the value of bashing the opponent and the flexibility of being monocolored are both very valuable
All that Clavileo needs is a consistent way of offing his own Vampires once they've attacked
That said, some have enough general applications that I've included them