This set is very confusing, but it gets less so when you find out there are actually two sets.
First to be issued was the one we show today, that came along in 1963, and was issued in strips of three really tiny cards. I have enlarged this one to show it off better. However if you look for them online it is harder to tell if it is a card cut from a strip or a larger card, so just bear in mind that the cards in this set are much browner than the later, larger, ones.
Those larger ones came along in 1966, and it looks like all the cards were re-issued as single cards, each one of which was the size of an entire strip. Like ours, the backs have a gravestone which is incised with "Monster Laffs", but the packaging bills them as "Monster Midgee Cards". And you got twelve cards for 5 cents, plus a piece of bubble gum, so they are true trade.
Both are from images supplied by American International Pictures, Inc., which was founded on April the 2nd, 1954, under another name, of The America Releasing Corporation. Their first film was "Operation Malaya", or "Terror in the Jungle", and though it was actually a documentary about the fight against Communism in Malaya, the poster makes it look more of a shock-horror-alien movie, which presaged their later output, for that was primarily low budget shock-horror-alien movies for the new "teenage" audience. Roger Corman started out with them and it is probable that some of his footage appears on these cards, and later on he would film many of the stories penned by Edgar Allan Poe.
Now I have not yet had time to check whether the two sets use the same pictures and numbering system, but I do know that there is a list of the large individual ones at Jeff Allender`s House of Checklists/MLS. He seems to think these were produced for Hallowe`en, as a bit of a cheap gimmick, and perhaps that is true, but once the artwork had been done Topps thought they could get double the value out of it.