From the Super Mario Wiki, the Mario encyclopedia
The Ladder is an item in the SNES and PC releases of Mario's Time Machine. After a scribe in Mainz mentions to Mario that he needs a ladder to reach an inkwell on a high shelf, Mario visits a nearby metalworker and asks him to lend a ladder for the scribe. The metalworker says that the scribe never returns anything, but gives Mario the Ladder regardless. Mario then brings the ladder to the scribe, who gladly takes it and uses it to grab to ink, elaborating that Johann Gutenberg wants to use it in the process of printing the Bible.