You can find a card from The List in 1 out of 5 Play Boosters
To play a full game, you need two sets, totaling around $32
For one, because most people will expect to be able to actually use the card they shelled money for, even if they dont plan on it
Along similar lines, the card is definitely worse in sideboarded games where most decks are more likely to draw that key piece of interaction, and the more copies of Unsubstantiate you play, the harder it is to sideboard them out when you decide theyre bad against your opponents post-sideboard configuration
common pairings include draw-sevens like Timetwister and cards that let you play lands from zones other than your hand, like Courser of Kruphix and Crucible of Worlds
Just like the Celes reveal last week, Zell Dincht is apparently being shown off now because it's the character's birthday - March 17