Pogoing backwards is a trick, presumably caused by a small bug in Keen's programming, allowing Keen to pogo backwards in Keen 4–6. The trick does not work in the first trilogy.
Pogoing backwards is simple.
- Start running in either direction.
- Jump, and keep holding the direction key.
- While in the air, quickly let go of the direction key you are holding, and hit the opposite direction key. Then toggle on the pogo, and press and hold again the direction key you started with in the beginning.
If you did this correctly and fast enough, Keen should now be pogoing backwards. When you let go of the key you are holding, Keen starts to pogo again in the normal fashion.