Vampire isnt the most relevant creature type, but its definitely one that you can support and Bloodthirsty Adversary is going to be one of the nicer cards for a Cube trying to do so
The black border ensures your theme or MTG character stands out among the thick crowd
Its about 75% committed to being an otter deck (why are there three copies of Waterspout Warden here?), and the rares arent half-bad, with the exclusive Bria, Riptide Rogue being an actual house of a card
So if you can share that ability with your Changelings using something like [[Agatha's Soul Cauldron]], suddenly they get to enjoy all the buffs after all
If it's not, they'll have to return the card to the bottom of their deck
That passive effect punishes cantrips, fetchlands, and any strategy built around card advantage