A Gunk card is a colorless Gunk sorcery named Gunk with cycling {4}. It has no mana cost, so you can’t normally cast it. It has no spell abilities, so if you do find a way to cast it, it won’t have any effect.

Cycling {4} means “{4}, Discard this card: Draw a card.”

A Gunk card’s owner is the player who first shuffled it into their library.

Gunk cards are not tokens. Treat Gunk cards just as one would treat regular cards. They can move between zones just like any other card and continue to exist for the duration of the game. At the end of the game, players should make sure to remove all Gunk cards from their deck.

Players can represent Gunk cards using objects from outside the game so long as the game state remains clear and understandable to all players. They might need to get creative. Since Gunk cards are shuffled into players’ libraries, those players should represent Gunk cards using objects that, while face down, are indistinguishable from other cards in their deck.

Playtest cards aren’t legal for play in any tournament format other than Mystery Booster Limited formats. On the other hand, we expect they will spice up a wide variety of non-tournament games (as long as everyone’s on the same page about using them!).

Playtest cards use a modified version of game symbols, such as {T} and {W}. These modified symbols should be treated as the standard symbols during play.

For many playtest cards, you’ll need to make a generous assumption that basic game rules would be updated to allow them to work. The Mystery Booster 2 Playtest Card Notes section (reproduced here in individual Gatherer rulings) provides guidance for fitting these cards into the existing rules structure.