Wikia

Prior to its official release, Shadow of the Colossus underwent several revisions. Originally, there were going to be 48 Colossi. Also, the game was initially referred to as Nico, a portmanteau of "ni", the Japanese word for two, and Ico, and originally featured a wasteland setting. Also, "ni" (ニ), was suggesting it being a sequel or follow-up to Ico.

As a result of these changes, there are several unused Colossi, most of which were prototype versions of existent Colossi that survived to the final version of the game. Other designs were discarded due to deadline constraints or to improve game flow.