Yes, Redmi Y2 does support the 1080p HD videos.
No. Redmi Y2 is not a waterproof mobile phone.
Yes, Redmi Y2 does have a dedicated MicroSD card slot. You can use 2 sim cards and a memory card at the same time.
No. You can not record slow-motion video with Redmi Y2.
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.