Painting

Paintings are objects from Super Mario 64 and its remake 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 certain Paintings are located in special themed rooms (for example Jolly Roger Bay's painting is in what appears to be an aquarium). 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.

Super Mario Odyssey
Paintings will return in Super Mario Odyssey. They serve the same purpose of acting as gateways to each of the game's playable kingdoms, but they are not the primary means of travelling to each kingdom. Instead, they are scattered across each location, often in hidden areas.

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.

Luigi's Mansion: Dark Moon
Mario gets trapped in a painting again in the game's sequel Luigi's Mansion: Dark Moon.

Trivia

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