I have very little info on Old Hag. I came across their debut demo on Bandcamp and the only thing I could really gather from there is that they're based in England.
On the musical front, Old Hag instantly brought me back to the '90s metal meets hardcore sound of Disembodied. Of the three songs on their demo, "Sinking" best represents what the band can do best. You get hooky death metal riffs along with some chunky mosh and a vocalist who shreds along with reckless abandon. The musicians in Old Hag have the kind of playing chops that makes the whole thing sound convincing.
This isn't some entry-level shit here. Old Hag are made of the real stuff.
Head to Bandcamp to listen to the entire 3-song demo for for further proof.