No. Vivo Y91 is not a waterproof mobile phone.
No. Vivo Y91 does not have the hybrid sim slot. It has 2 dedicated slots for sim cards and a dedicated slot for the MicroSD card.
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.