The most common source of silver-bordered cards like these ones are not MTG crossovers, but instead the joke sets or Un-sets, that are released every once in a while
I felt the layout was silly enough that what the card did should be very straightforward
Lets demonstrate this by taking a look at a fairly average Sealed deck I recently played that had 17 lands: Why is this deck playing 17 lands rather than, say, 16 lands (-1 Forest, +1 Arrogant Poet) or 18 lands (-1 Tenured Inkcaster, +1 Swamp)
Skyclave Cleric, on the other hand, is a legitimately workable sideboard card
Just as fixes were made, Memory Jar came out and caused more concerns about unfair play
11 Mario Stadium Best Photo Contest Chansey As with many of the most valuable Pokmon cards, this card came as part of a limited run designed to be awarded to competition winners