They protect your cards from moisture, dust, and oil stains, keeping your cards in pristine condition through extended use
If heads, you will remove the Burn Counter
Theres also Prosperous InnkeeperProsperous Innkeeper, Ravenous SquirrelRavenous Squirrel, and Moldervine ReclamationMoldervine Reclamation, as well as some aristocrat life drain happening, with Zulaport CutthroatZulaport Cutthroat, Nadiers NightbladeNadiers Nightblade, and Bastion of RemembranceBastion of Remembrance
Even the rarest card loses market power if it has whitening, creases, or edge wear
You can only use them if you are doing a Limited event using Mystery Boosters, or are participating in one of the MagicCon Unknown Events that has its own unique playtest cards
So much so that its unlikely to return outside of supplemental sets