Step Stool

It is a building tool. Hold up while standing still and you gain two tiles of upward placement reach, which is the difference between a smooth build and constantly stacking dirt pillars under yourself. It does nothing for downward reach.

Standing on it makes your hitbox taller. Anything that would have passed over your head now connects, so it is a liability in a fight and you should not leave it extended while something is chasing you. It also refuses to deploy in tight spaces, needing a couple of tiles of width and about five of headroom.

Surface chests are the common source, along with wooden and pearlwood crates, and the Skeleton Merchant carries it on a waning crescent if you would rather buy than dig. It later feeds the Hand of Creation, which is where most players end up parking it permanently.