Yes, Redmi 6A does have the night mode. It also has eye protection mode.
No. Redmi 6A does not have the gorilla glass protection.
Yes, you can play PUBG on Redmi 6A.
No. Redmi 6A does not have the removable battery. It has a nonremovable battery.
The Redmi 6A is a fairly good update to the Redmi 5A, which itself was barely any different compared to the Redmi 4A. You now get a tall screen, better processor, and improved polish overall.