Yes, Vivo Y91 does support the face unlock. It also has a fingerprint scanner.
Yes, Vivo Y91 does have the OTG support.
Yes, you can play PUBG game on Vivo Y91 easily. Please check the following video which will give you more idea about the gaming performance on Vivo Y91.
Yes, Vivo Y91 does have the virtual Gyroscope sensor.