No. Redmi 6A does not have the front camera flash.
Yes, Redmi 6A can play Full HD videos without any problem.
Yes, you can play PUBG on Redmi 6A.
Yes, Redmi 6A does have the night mode. It also has eye protection mode.
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.