Yes, Redmi Y2 does support the PUBG game.
No. You can not record slow-motion video with Redmi Y2.
Yes, Redmi Y2 does have the fingerprint scanner & face unlock, too.
Yes, Redmi Y2 does have the portrait mode for the rear camera. The front camera does not have the portrait mode.
The Xiaomi Redmi Y2 is a slightly better attempt at a selfie-focused smartphone than the model it replaces. It has proven hardware that is capable of delivering a smooth user experience, plus MIUI 9.5 which has a lot of added features.