These cards were so insanely overpowered (or in R&D slang bah-roken) that I figured it out without even needing a playtest
There are several versions of the card, each of which lets you choose from several unrelated effects, like flipping one of your opponent's cards over
You're removing the opponent's field and gaining a Life card, making it almost impossible for them to win on the upcoming turn
For seven loyalty, you get an emblem that lets you not only untap all of your permanents during everyone elses untap steps, but also draw a cards during their draw steps
At the end of your upkeep, if Death Spark is in your graveyard with a creature card directly above it, you may pay one colorless Mana to put Death Spark into your hand. This kind of graveyard specificity was unheard of before Death Spark
A random Secret Illustration Rare can appear in 1 in every 67 booster packs, while a specific SIR can be pulled in 1 in every 335 booster packs