With an original print run in 1993 of approximately 1,008 for each card, they are incredibly rare and desirable
Left unchecked, it transforms into a powerhouse that snowballs card draw from damage
The big issue with Big Grim is that he tends to get dealt with, and once he does his cost isn't super cheap meaning he can get hated out of the game
(10/4/2004) The new blocker does not trigger any abilities which trigger on creatures becoming blockers, because the creatures were already blockers and the simple change of who is blocking does not trigger such abilities.
Its a very effective way to control their draws, so its only been printed on two cards: Mesmeric Sliver and Spin into Myth
Per PokeBeach, the cards were likely stolen during the production phase, when the Secret Rare cards are printed separately than other cards in the set due to their texture and then sent over to sorting machines, which places the cards into individual booster packs