During a recent Iwata Asks interview, some of the Splatoon development team revealed that they had actually forgotten about the water gun in Super Mario Sunshine until late in the development process. Splatoon utilizes several weapons which perform similar functions to the F.L.U.D.D. device, which was used by Mario in the older game.
Satoru Iwata asked developer Hisashi Nogami about Super Mario Sunshine, pointing out that it had also used the unique element of using a pump to spray water.
"Over ten years ago, we had a game called Super Mario Sunshine. A unique element of the game was using a pump to spray water. Did this game come to mind?" — Satoru Iwata
Nogami replied that they " get asked that a lot." He then said that they only remembered about the water gun concept later on.
"We only remembered it later on. Like, "Oh yeah, there was a water gun in Super Mario Sunshine." As Nintendo employees, that’s pretty embarrassing." — Hisashi Nogami
The interview revealed several tidbits of information about Splatoon's development, such as the fact that the game had originally starred rabbit-based characters rather than squids.
Splatoon is due for release on May 28th, 2015, exclusively for the Wii U.