One makes you smaller is the easiest way to acquire multiple size downs, and while you can exit the crawl space using listed minimums, it requires a lot of patience sometimes.Use 4 size downs, 2 speed, and crash into the floor below the entrance ladder or 3 size downs and the left and right walls using flight.Blank Card + XXI - The World?, Clear Rune + Rune of Ehwaz, We Need to Go Deeper! and Mom's Shovel offer consistent methods of creating crawl spaces.This will always bring you to an error room, even when all other methods stop working.
The I AM ERROR room can be reached by leaving a Crawl Space through an unintended direction.Using Teleport 2.0 when all rooms on the floor have been explored (including the Secret Room(s), Super Secret Room(s), and the Devil Room or Angel Room) sends you to the I AM ERROR room.Telepills have a very, very small chance of teleporting Isaac to the I AM ERROR room.At least 2 uses of Cracked Key are needed to enter if you don't have access to Red Key. No red door outlines will appear on the normal floor's boundary walls, meaning the I AM ERROR room can only be entered from another Red Room.Using Red Key on the 13x13 boundaries of the map will create a 1-way door to the I AM ERROR room, and displays no icon on the map upon opening.Undefined is the simplest method, as it has a decent chance to teleport the player there.The only items/effects that can bring Isaac to the I AM ERROR room are Telepills, Undefined, Teleport 2.0, Red Key and Blank Card + ? Card.