In Jazz Jackrabbit 2, when playing as Spaz Slackrabbit you can perform a technique called the Wall Climb.
To do this, you must find a ceiling that you can reach by jumping. The tile for this ceiling must be flat, solid, and take up the entire square. First, you must jump at the ceiling so that your head hits the bottom of the tile. Just as your head hits the ceiling, perform a buttstomp by pressing Down. While you are paused in the air, you must double-jump before the buttstomp actually executes. If done correctly, you will get sucked into the ceiling.
Next, what you want to do is find a partner you can collide with. This means that if you are playing CTF and someone is on the same team as you, you cannot Wall Climb with them since you can't collide. Once you find someone, that person must enter the ceiling in the same spot as you. When both of you are stuck in the ceiling in the same place, you will begin to ascend the wall. Over local, this will be very quick, but over the internet it will take some time due to the amount of delay in sending data between computers. Once you reach the top, you will be ejected out of the wall and will be standing on the floor at the top.
And that's how you Wall Climb!