Painting Demons

The Painting Demons were the central villains of a short horror comic strip in Suspense #8/8 of 1951 - published by what what become Marvel comics during their relatively early years, long before they decided upon a true shared universe and as such most stories were in the style of Tales From the Crypt or Twilight Zone rather than the superhero fantasy Marvel is known for in the modern era.

History
The Painting Demons are a collection of hideous monsters depicted in a strange painting purchased one day by an unwary Robert Denning when he went to a mysterious auction - the painting soon made him and his wife uneasy, with Denning going as far as believing it to be alive.

Eventually Denning reaches to a distracted woman in the painting only to be mystically sucked into the painting himself, he helps the woman inside the painting to fend off many horrible monsters as she made her escape into the hills in the strange dimension.

Meanwhile in the real world Denning's wife advances on the painting with the intention of slicing it up (due to her fear of it), however she could hear Denning from within and reached out to touch the painting - this caused her to be transported to the dimension and Denning to return to the real world in her place.

Unaware of the fact his wife was trapped in the painting Denning quickly sliced the painting up, destroying it - the ultimate fate of Denning is unknown, as is that of his wife.

Abilities
The monsters in the painting were wild, alien creatures with varied animalistic abilities such as sharp teeth, fangs, claws and monstrous violence - they were capable of being killed by blunt force (such as a rock to the skull) but were very numerous and driven by a near-mindless desire to torment and harm any that they came across : so great was this desire to fight and kill that they would attack each other and greedily feed on their fallen brethren like wild animals.

Trivia

 * the monsters depicted in the painting are mysterious but clearly of some kind of hell-realm, hinting at a connection to Mephisto or the Nightmare Lords (though they could be of any number of similar realms).
 * while not officially labelled as demons the inhabitants of the painting fit all criteria, being extremely vicious extra-dimensional creatures that inhabit a reality which is extremely hostile to human life.
 * the origin of the painting is left a mystery and its destruction is unlikely to fully seal away the demons, as of the modern era however they have never been refered or seen in Marvel.