Rules Card

The Rules Card is a special card which randomly displays cryptic statements on the screen similar to a Fortune Telling Machine. It is unlocked by completing Glass Cannon (challenge #11).

Effect

Upon activation, displays one of the following messages:

CHUB DISLIKES SMOKE!	Referencing the trick in which Isaac can drop a Bomb in front of a charging Chub to have her swallow it. Reference to Zelda 1 and 'DODONGO DISLIKES SMOKE'.
A PIECE OF PAPER IS YOUR GUIDE	Possibly refers to the Missing Poster, the choice between The Polaroid and The Negative after defeating Mom or the card itself.
THE WALLS WILL HARDEN OVER TIME. TIME IS THE ESSENCE	Presumably referencing the Boss Rush that occurs if Mom is beaten in under 20 minutes, and/or the Hush fight that is accessible if Mom's Heart or It Lives! is beaten in under 30 minutes.
A DARK MARKET LIES UNDER YOUR FEET	Presumably referencing the secret trapdoors occasionally under rocks and the Crawl Space that leads Isaac to the Black Market, a room which sells Shop items for Hearts rather than Coins.
SOME DOORS REQUIRE A BLESSING. CARRY THEM WITH YOU	Refers to how to open the large golden door on Chest and the Dark Room, by gathering two Key Pieces from the Angels.
DENY HIS GIFTS TO ATTAIN YOUR REWARD	References how skipping a Devil Room gives the chance to gain access to the Angel Room.
SLEEPING GATEKEEPERS WILL NEED TO BE AWOKEN WITH A LOUD SOUND	Possibly referencing how Isaac can use bombs on the Angel statues in order to awaken them. Reference to Zelda 1.
ROOMS MAY YIELD MORE THAN YOU EXPECT. EXPERIMENTATION IS KEY	Unknown, possibly referencing Secret Rooms or the trapdoor and bed in Isaac's room, or tinted rocks and other breakable objects.