I couldn’t choose just one! So I chose one from my three favorite decks: my Legacy Elves, my standard Vampires and my standard haste-undying Red/Green Aggro.
Priest of Titania is illustrated by my favorite artist, is great for any elf deck, and perfect for trolling your friends with elf decks. Bloodline Keeper is just a badass vampire. Hellrider is a great aggro card for any situation (and is just a badass devil).