Boulder

The Boulder is a placeable 2x2 block added in 1.1 patch. Whenever they are unsupported or you use a pickaxe on it, it will roll and deal massive damage.

Boulder traps are naturally occurring in caves of worlds generated after 1.1 patch. These consist of a single boulder in the ceiling supported by several Active Stone Blocks and wired to a Pressure Plate. If the player mines the Active Stone Blocks or someone stands on the Pressure Plate, the boulder will fall and roll towards the player at a fast speed; if the player is hit, they will take massive damage. As shown in the video, a boulder will always roll to the left if possible. When there's no space for it to go left, the boulder will roll right instead.