A Ladder is an environmental object which can be interacted with by Kirby and other playable characters. Using a ladder will allow Kirby and co. to quickly climb up or slide down the ladder's length, with the former action being generally quicker than Hovering. Ladders first appeared in Kirby's Adventure and have since featured in most main series Kirby games.
Kirby will automatically mount a ladder if the player is holding up on the D-pad/analog stick/circle pad while Kirby is touching one. While on a ladder, Kirby will be unable to perform any action other than climbing up or sliding down it, but can dismount if the player inputs left or right. In Kirby's Return to Dream Land and subsequent main-series titles, Kirby and co. can carry items while using a ladder, making ladders often necessary for solving certain puzzles, since Kirby and other characters cannot fly or hover while holding items.
In Kirby and the Forgotten Land, ladders serve a much more crucial role in Kirby's journey, since Kirby's hovering height is limited.
Climbing a ladder in Kirby's Adventure
Artwork of Kirby climbing a ladder from Kirby: Nightmare in Dream Land
Screenshot of Kirby using a ladder in Kirby & The Amazing Mirror
Screenshot from Kirby's Epic Yarn
Screenshot from Kirby: Planet Robobot
Screenshot from Kirby Star Allies
Screenshot from Kirby and the Forgotten Land