mtg booster box duskmourn Duskmourn: House of Horror Players may even face the evil within themselves—but they will be rewarded for their bravery Magic the Gathering: Duskmourn Collector

Eeveelution collectors building their complete Eeveelution card collection

Historically, this came about because Wizards R&D would use B for black and L for land, so U became the shorthand for blue and it's been that way ever since

Maybe gen 1 trainer mechanics(supporters as item cards)

Sword of Truth and Justice is another one that is pretty good with Venser as the commander since it gives him (conditional) evasion, proliferates, and adds +1/+1 counters to grow your creatures which the deck has very few ways of doing, but I absolutely would not spend $30+ for the card, it's not that good

If all players can't agree if the card qualifies, you may ask an outside person for a final determination