Wire

Wires are pretty rare objects in the Mario series that are used for housing electricity and swinging on.

Donkey Kong Jr.
Wires first appeared in Donkey Kong Jr. on Stage 3 where Mario activated Sparks which would then travel across in the wires in an attempt to shock and defeat Donkey Kong Jr. Junior must jump over the Sparks that fall from the wires while climbing the Ropes to eventually reach the top with Mario, his father and the Key.

Donkey Kong (Game Boy)
Wires reappear in Donkey Kong for the Game Boy but this time they are attached to telephone-like poles. Mario can grab on and move across wires and can also do the Wire Spin to either do a small jump or a large jump to get to areas he could not reach. The wires are sometimes either facing vertical or horizontal which can help make him go up higher or go over huge gaps but Sometimes wires have Sparks on them which will electrocute Mario causing him to lose a life.