Impossible Bullet Trick
The Impossible Bullet Trick, presumably caused by a small bug in Keen's programming, allows Keen to ride on a bullet. This bug requires careful timing to exploit, and only works in Keen 6. It is not an officially documented trick as with the Impossible Pogo Trick, but named as such by fans upon its discovery due to its comparable difficulty and niftiness.
The trick allows the player to fly upwards, until hitting the ceiling or otherwise interrupting the manoeuvre (such as by jumping — although it is possible to walk a couple of pixels left and right before "falling off" the bullet). It can be very helpful in levels such as Bloogton Tower and getting the Grappling Hook in the First Dome of Darkness, although technically it is considered cheating.
Steps to reproduce
It takes some practice to get the timing right:
- Jump in the air.
- As you start to fall, shoot downward.
- If done correctly, when you land, you should be standing a tile above the ground.
- Shoot up, and you will fly up with your bullet.
If you are standing against a wall when you perform this trick, shooting into the wall will also raise you by a small amount.
The technicalities of how this trick works are at least partly unknown, as the source code for the games has not been made available. The explanation likely revolves around the fact that Keen's bullet has the collision property of the Gik or Goplat. The bug means that Keen can stand on his shots, but the only place this can occur is just after a bullet has hit a tile, when it has stopped moving but has not yet become a "zapped" bullet. When Keen lands on the bullet and it vanishes the game become confused as to where the bottom of Keen's clipping box. When Keen fires a second shot, if that shot is in the same vertical column as he is (Shot upwards or close to a wall), the game reads Keen as standing on it and clips him on top of it.
The Impossible Bullet bug is used extensively in a walkthrough for Keen 6 in which the player gets no points, exploits various clipping errors, etc.