Slime Block

Landing on slime bounces you back up and wipes out the fall damage completely, which is the whole reason to craft it. A layer at the bottom of a hellevator turns a fatal drop into a landing, and a short strip of it works as a trampoline for reaching a ledge without a hook. Hold down as you land if you want to stop instead of bouncing.

The bounce catches enemies too, so flooring an arena with it means things ping around the room instead of walking at you. It is see through and it drips when you step on it, so most builds use it for effect and keep it out of surfaces they walk on daily.