Painting

Paintings are an object from Super Mario 64 that work like portals. They are used to get to the many levels in the game.

Super Mario 64
Paintings in Super Mario 64 are used to travel from Princess Peach's castle to the game's many levels. Such as Bob-omb Battlefield each Painting is located in a different themed room (for example Cool, Cool mountain is located in a snow themed room). Paintings frames are also different colors (but some have the same too).

Super Mario 64 DS
Paintings return as portals in the Super Mario 64 remake, serving the same purpose. One noticeable difference is that the Jolly Roger Bay painting is replaced by bubbles instead of a galleon from the original.

Luigi's Mansion
A single Painting makes an appearance in Luigi's Mansion where Mario is trapped. At the end of the game Luigi rescues him from the painting and he goes flying towards him. Mario gets trapped in a Painting again in the games sequel Luigi's Mansion Dark Moon.

Trivia

 * In Wet Dry World's painting, the Skeeter is shown to be green although they are actually an aquamarine color.