For those who play the game without a controller like me, I will tell you how to beat the Glott with mouse and keyboard.
The easy part is when he turns RED. You should press shift and get to his back, you have chances of 1 or 2 hits. The hard part is when he turns YELLOW. The game doesn't tell you which button to press. I press mouse wheel, shift... Nothing happens.
Here is what i found.
When he turns yellow press the right click then left click on the mouse quickly.
After you dodge the attack proceed with quick time events and do the same thing until you kill him.