Deku Scrubs are plant-like creatures that inhabit the forests of the Legend of Zelda universe. The Deku are first seen in Ocarina of Time. They are apparently made of wood and can perform different activities within the game’s universe such as selling you items or attacking strangers with their ability to spit Deku Nuts.
Besides the Business Scrubs, most Deku Scrubs (especially the red-colored ones) are hostile towards Link in Ocarina of Time. In Majora's Mask, there is a whole community of Deku residing in Termina. It is seen in Majora’s Mask that they also have their own palace from where the Deku King rules his servants. The palace is heavily protected by a guards and possesses two side gardens that Link uses to sneak in. If the guards catch a trespasser, they will immediate kick them out.
The Deku are able to shoot Deku Nuts and bubbles through their snouts. In Majora's Mask, they are also seen to be dainty enough to skip across water for five steps. They can also launch themselves from flower pads and temporarily fly. In the beginning of Majora's Mask, Skull Kid transformed Link into a Deku Scrub. When Link finally healed himself, he was then able to possess the Deku Mask, which he used to transform back into a Deku whenever he desired.