2.39:1, as noted in the Violent Night Technical Specs on IMDb .
WEB-DL (lossless rip from a streaming service like Amazon or Apple TV)
In the context of scene releases, a "PROPER" usually indicates a fix for a previous release that had technical issues. However, if you are looking for technical specs to ensure you have the right version, here is what that specific file signature entails: Technical Specifications 2160p (4K UHD)
10-bit SDR (Standard Dynamic Range). Note that while many 4K releases are HDR, this specific version is tagged as SDR.
x265 (HEVC), which is standard for 4K content to maintain high quality at smaller file sizes.
The "proper piece" for a release with the filename usually refers to a NFO file or a specific subtitle file that matches the exact timing of that high-definition WEB-DL rip.