The ending combo
The "End Combo" (known as the "ERRRROR ERR@R ER*^#%R COMBo" in the combo display) is the hidden combo in Little Inferno. It cannot be performed until the last catalog is obtained. Performing this combo will cause the player to enter the second segment of the game.
This combo can only be used once and will not work if used after the first use. It also will not show up on the combo list.
The "End Combo" consists of the four items that the character sends Sugar Plumps over the course of the entire game; the Broken Magnet, theJar of Fireflies, the Toy Exterminator, and the Fashionable Sunglasses. Sugar Plumps states in a few of her reply letters that there's "something special" about the things you send her, asking the player if "he felt it too". Near the end of the game she says in one of her letters that there is something special about the way the items "glow" together when burned, and encourages you to perform the combo in several different letters from then on, always ending them with "It is time." After you burn these things together, you receive an Error message in the form of a combo and your Little Inferno beings to have a meltdown, causing it to fall apart and eventually explode, burning your house down. When your Little Inferno is having a meltdown if you click on the Tomorrow Bucks and the Tomorrow Stamps they will break and money and stamps will erupt out of it. When both burned the face's eyes will begin to open, black smoke will come from the sides. The view changes to show your house exploding which will send you into the second part of the game. Once achieved, the house will explode.
Trivia
Not only do these things create the End Combo when burned together, but when burned separately, they interact with the fireplace itself. (Broken Magnet makes the cogs turn faster, Jar of Fireflies makes the face's mouth open, Toy Exterminator makes the face glow red, Fashionable Sunglasses can be worn by the face).