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Deep Cheeps (originally parsed Deep-Cheeps) are a special variety of Cheep Cheeps that are first found in New Super Mario Bros. They appear to be regular Cheep Cheeps, except for the fact that these creatures are green and will swim in the direction of Mario or Luigi in underwater levels depending on the direction they swim in. Deep Cheeps will only give up pursuing Mario or Luigi provided the latter ones swim behind and past the fish foes.
Super Mario series
New Super Mario Bros.
New Super Mario Bros. Wii
In New Super Mario Bros. Wii, Deep-Cheeps are slightly more common. One appears in World 1-4 along with a Mega Deep-Cheep. If Mario and co. keep staying in the area, another pair of green fish enemies appears. Deep-Cheeps can also be encountered in the second part of World 8-4.
In this game, their lips have become pink, matching the current depiction of a Cheep Cheep's, rather than keeping the red-orange colored lips they and Cheep Cheeps previously had in New Super Mario Bros. Their dorsal fins and tails have also become yellow, as opposed to white. There is a more relentless enemy similar to Deep-Cheep known as Spiny Cheep Cheep.
New Super Mario Bros. 2
New Super Luigi U
Though Deep Cheeps do not appear in New Super Mario Bros. U (despite them receiving official artwork for that game), they still appear in New Super Luigi U, behaving the same as in previous games. Their only appearance is in Cheep Chomp Chase.
Super Mario Maker / Super Mario Maker for Nintendo 3DS / Super Mario Maker 2
Deep Cheeps reappear in Super Mario Maker, Super Mario Maker for Nintendo 3DS, and Super Mario Maker 2. They aesthetically replace green Cheep Cheeps and Blurps in the New Super Mario Bros. U style, except that they no longer chase the player due to the green Cheep Cheeps and the Blurps from other styles not being able to chase Mario. Furthermore, the voice heard when placing Deep Cheeps onto the course just calls them Cheep Cheeps.
Mario Party 9
Names in other languages
Years before Deep Cheeps debuted, green Cheep Cheeps had existed in the Mario franchise in several games.
The Paper Mario series has also featured green Cheep Cheeps that are not Deep Cheeps.