Img_8356mp4 -

: Telegram channels and file-sharing sites often list files like IMG_8356.MP4 alongside other sequential media (e.g., IMG_8355, IMG_8357).

: Short for "Image," used for both photos and video files.

Unless you are referring to a specific "creepypasta" or an "Alternate Reality Game" (ARG) that uses this specific number as a clue, "IMG_8356.MP4" remains a placeholder name for a standard video file.