Being highly non-linear, the Katamari series is quite easily given to hiding references to Namco, other video games, or even the series itself. Often, simple objects in game will be arranged as a reference of some kind and can either be out in the open, or can be hidden and only seen under certain conditions.
Easter Eggs in all of the games of the series include:
- The NA, M, and CO save files
- Moving objects and characters often represent a katamari being rolled. This occurs in stages for all of the games.
- The "Jumbomen" may be a reference to the classic Japanese TV hero, Ultraman.
- If you hit the Katamari on an item at a certain angle, the katamari will float in midair. It will not fall back on the ground until you hit another item. You can see a video of this on youtube.
- In the Racing level, several cousins can be seen rolling objects in around a house, referencing the race that takes place during the level.
- In the same level, a "Happy Flower" can be seen sticking out of a duct stuck in the ground, reminicent of the Pirahna Plants of the Mario Bros. series
- An arcade game machine plays the Pac-Man theme when rolled up
- On the sumo-wrestling level, there is a copying machine with Prince on the top, and Slip, a flat version of Prince, coming out of the tray.
- On the Make a Planet 3 level, there are several moles surrounded by "funny hammers", similar to the Whack-a-Mole game.
- In Make a Planet 5 near one of the starting areas, there is a female ghost that rises up and down out of a well, like the character Okiku in the Japanese folktale Banchō Sarayashiki. (This is also reminiscent of the character Sadako in the Japanese horror movie Ringu.) The same "ghost" also appears in the school as fast as possible level, where it rises up on down out of a toilet in the school restroom.
- Another example is the Tsuchinoko, a snake cryptid which can be found in a few levels, notably in the flower stage (popping in and out from a pink flowerbed), the zoo stage (one is hidden in the small bushes where you start and another is in a jar near several cobras) and Make a planet 3 (three are pulling a child who is sitting on a skateboard all around outside the level). In reality, only a few people claim to have seen this snake, and so it is very hard to find in these stages
- There is a creature very similar to a Kappa in the game (actually named as a Kappa in the Japanese version). In fact, the sumo-wrestling level contains two “kappa” in the large pool near the opponent.
- In the flower level, a lady titled 'God' when rolled up can be found in the pond with a bear.
- The Nazca Lines that you can pick up may be a reference to the earlier Namco game Xevious.
- There are Pac-man arcade cabinets that play it's theme when you roll it up in the later city levels.
- The Coolhouse stage has many Xbox 360 consoles and controllers in the house and around the pool , including a collection of controllers arranged that spells out 360.
- Re-entering Egg School as Marcy makes the hiding cousin the Prince.
The "Hollywood" sign (seen in levels with a large Katamari) is sometimes different, and spells other words like "woody doll"