This is a House Ad for DEMON!, another entry in Portman's line of Marvel horror reprint titles published under license in the late 1970s.
I've never seen a copy of this one so this ad was the first I'd heard of it. I assume, like the others, it pulls material from the seventies US scare-fare magazines.
By accident or design, Marvel UK found itself competing against its own licensed reprints so, when Dez took the helm, he cancelled the deal with Portman and these mags ended. Something of a shame as he didn't launch anything similar.