Low-quality versions recorded in theaters (best avoided if you value your eyes and ears).
While sites like World4uFree or Bolly4u are popular for 300MB MKVs, they carry significant dangers: Dangers of Illegal streaming | FACT
Unlike older formats like AVI or MP4, the Matroska (MKV) container is incredibly flexible. It can hold multiple audio tracks (perfect for dual-audio Hindi/English movies) and built-in subtitles without significantly increasing the file size. The Magic of HEVC (x265) Encoding
Noticeable loss in visual detail (grainy images, artifacts), muffled audio, and "hard-coded" watermarks from the source website. Popular Sites & Their Risks