Thanks to GreatZero for this idea. You have made some glorious contributions to science and for that humanity is grateful.
Alternative middle of The Fall
Chell jumped from the catwalk and through her portal. She came out of her other one that was on the slanted panel. The Aperture Science logo had fallen out of the large circle that she flew through. She hit the wall then walked through the door that automatically opened.
A prerecorded message clicked on as she entered the room. "Those of you testing the repulsion gel follow the blue line on the floor. Those of you that signed up to be injected with praying mantis DNA I've got some good news and some bad news. The bad news is we're postponing those tests indefinitely. The good news is we have a much better test for you, fighting an army of mantis men. Pick up a rifle and follow the yellow line. You'll know when the test begins."
Chell shuddered as she thought about the mantis men. They had all been normal human testers and now some odd hybrid mix of man and insect. What did they think would happen? Superpowers?
She walked out of the room and jumped off of the broken platform. Then she went over to the elevator. A preying mantis was sitting on the button. She swatted it off then pressed it. The lift started going up. She shot a portal on the slanted panel and walked down a few stairs then jumped and shot her other portal on the ground.
As she started flying out of the portal something grabbed her leg. She looked back and saw a green arm holding her leg. The vault behind it was open. It dragged her in and ate her piece by piece.