16 cards where the set is “j21” and the cards are can only be conjured in their set

Light of Hope (Jumpstart: Historic Horizons #777)
Stormfront Pegasus (Jumpstart: Historic Horizons #778)
Swords to Plowshares (Jumpstart: Historic Horizons #779)
Force Spike (Jumpstart: Historic Horizons #780)
Kraken Hatchling (Jumpstart: Historic Horizons #781)
Ponder (Jumpstart: Historic Horizons #782)
Dark Ritual (Jumpstart: Historic Horizons #783)
Duress (Jumpstart: Historic Horizons #784)
Reassembling Skeleton (Jumpstart: Historic Horizons #785)
Assault Strobe (Jumpstart: Historic Horizons #786)
Lightning Bolt (Jumpstart: Historic Horizons #787)
Shivan Dragon (Jumpstart: Historic Horizons #788)
Fog (Jumpstart: Historic Horizons #789)
Giant Growth (Jumpstart: Historic Horizons #790)
Regal Force (Jumpstart: Historic Horizons #791)
Tropical Island (Jumpstart: Historic Horizons #792)

Though this query has ended, its relics still slumber in New Argive.