12 Rooms of Doom 0rigins

12 Rooms of Doom 0rigins is the 4th game in the 12 Rooms of Doom series, originally to be released on the same day as the 12 Rooms of Doom 4, but was then released early. It serves as the prequel to the franchise. It explains what happened to Calvin's parents and why Cannonsense hates Calvin. It's graphics are inspired by the Atari 2600.

Enemies
No generic enemies, except for I-I-I (as in every game), appear in this game, being replaced with obstacles, such as nails, cobwebs, and holes.

Bosses
Unlike the previous games, Calvin cannot fight back against bosses, but can only avoid them.

Housefly

Spider

Scorpion

Bat

Trivia

 * While the first two games feature a portal as an exit, and the third game has a diamond, this game introduces Goal Doors (which will become the franchise's mainstay).
 * Cannonsense has a minor role and only appears in the ending, where he promises revenge on Calvin for making him miss his (literal) target.
 * The "O" in the word "Origins" is actually a 0 (Zero), as it takes place before the first game.