I would recommend getting the singles, since both Mystery Booster sets are pretty expensive, while most playtest cards cost under a dollar
In a format where most win attempts involve instants, sorceries, or noncreature spells, these cards offer high-impact answers for just 1 mana
The tricky part comes in narrowing your card pool down to what you can afford versus the purpose of each card inside the deck
Note: If a character is summoned they are out of play (their ink is still drying) until the next turn unless rules state otherwise you gain access to them in the Ready phase of the next turn
His Mardu colour identity is important too, allowing the deck to break outside of the usual Rakdos colours for vampires and include all the white vampires that have been printed in recent times, as well as providing access to enchantment removal which historically black and red have struggled with
7/7 Card Details Set Mystery Booster Playtest Cards 2019 (CMB1) Rarity rare Colors G Artist Damian Tedrow Collector # 85