The alternate art of the Call the Bloodline promo is beautiful, and it's still the preferred artwork among players who want this card for their decks. Even when this was a 10-cent uncommon back in late 2016, it was a $1.50 foil due to demand from Standard and EDH Vampire Tribal players. In the years since, a Commander deck full of Madness cards was printed, increasing the demand for this card.
Call the Bloodline is often used in a combo with Indulgent Aristocrat. Pay the one mana and discard a card to make the Vampire Knight token. Indulgent Aristocrat can then use his ability to pay 2 mana to put a +1/+1 counter on each Vampire creature you control. It's a slow combo for Vampire EDH decks, and it can only be used once each turn, but it can pump your creatures enough to win a game.
You would think that Call the Bloodline would be an auto-include in Vampire Tribal EDH decks. Indeed, the Enchantment is played in many Vampire decks led by Olovia, Mobilized for War and Olivia Voldaren. But in the deck that could probably use Call the Bloodline the most, the Vampire Legend created to fuel Madness themed decks, Anje Falkenrath decks rarely run it. Perhaps, newer players of EDH don’t know about this card, or can’t make room for it?
In any case, Call the Bloodline is a very good card. It’s proven a bit too slow for the eternal competitive formats like Modern and Legacy, but it’s good in EDH, and probably underutilized. Being that you can only activate the ability once per turn - although you can also use it on each opponent’s turn, too - it’s a very grindy card. It also needs a deck that gains value from discarding, but there are plenty of those to go around. While it's far from being one of the more valuable Friday Night Magic promos, often available for under a dollar, the Call of the Bloodline promo is one that will be sought after for years to come.