(As written in the N in-game help:)
- According to legend, in pre-robotic times there existed a race of large, spikey stone dolts whose complete invulnerability and hereditary hatred of heroic italian plumbers led to their persecution, and eventually to extinction. (A reference to Super Mario.)
- Thankfully they've been recreated, in robot form, and 3 of their 4 sides have been rendered harmless.
A thwump is basically a square block with one blue deadly electrified side and three non-electric sides. A thwump's line of sight is rather narrow, and extends to the adjacent row or column. This means you can draw thwumps down without ever being in any danger if you stand in the right place. Downward and upward-facing thwumps can only see the ninja in the column the deadly side is in, and the adjacent columns to it. Left and right-facing thwumps can only see the ninja in the row the deadly side is in, and the adjacent rows. However, thwumps can't see behind themselves, so you're safe if you're back there. Here's a picture to clarify things:
The area that the thwumps can see is shown in yellow. The ninja is safe because the thwumps cannot see him. If the ninja were to move into one of the yellow areas, the thwump would rush forward in the direction of the arrow in an attempt to electrocute the ninja or, at least, crush him. Upon contact with a tile, the thwump will then slowly return back to its original position.
Keep in mind that thwumps only have one deadly side. You can walljump off of thwumps, and in some cases even ride them. Also keep in mind that they do not collide with doors or other objects, so you cannot hide behind these, unfortunately. And also, watch out for thwumps positioned with a wall at their back. If you ride them, it's possible to get crushed against the wall. However, if you are not dead center against said wall and are positioned correctly, it is possible for you to instead be squeezed by the thwump and be blasted off at great speed. This trick is very frequently employed in 83-3: Bricklayer (by xRyuenjinZeroEX) by highscorers.
- 83-3: Bricklayer by xRyuenjinZeroEX
See this article to learn about the strange but usually helpful tricks to help you master the usage of thwumps.