I'm not entirely sure I can adequately express how stupid The Diabolical is without at least one significant spoiler, but I'll give it my best shot.
At first glance, writer/director Alistair Legrand seems to present a haunted house flick. Madison (Ali Larter) and her children Haley (Chloe Perrin) and Jacob (Max Rose) are being tormented by horrific humanoid apparitions. They seem to come in three forms: a bald man in a white jumpsuit whose face we never quite see; a holographic version of the same man that can pass through walls to grab at people, at least until it's convenient for the plot that it be stopped by holding a door shut; and a decomposing body that crawls around and pulls off layers of its flesh. For some reason, she does not immediately leave the house.
Eventually a reason is supplied. On one visitation the thing manages to grab Haley and Jacob, burning them where they were grabbed. After that, they collapse into creepy makeup effects and comas whenever moving more than a few feet from the house. But still, no explanation why she thinks they can just keep living in a house where some guy pops in every so often to take his skin off. Especially when she's behind on the mortgage and has an extremely generous offer from a representative of a holdings company (Patrick Fischler) to buy them out rather than simply foreclosing.
I can understand why, having made the stupid decision to stay in the house, Madison is embarrassed to admit it to her high school physics teacher boyfriend, Nik (Arjun Gupta). But when he eventually finds out, he pulls some strings to borrow cameras and sensor equipment from his old research lab job, which I guess are somehow better than the equipment used by the professional parapsychologists Madison had brought in.
There are a number of different possibilities the script raises about what's going on. Most of them are red herrings wasting time that could have been better spent on making the real story less distractingly stupid. There's a lot of talk about Madison's ex-husband -- Haley is convinced that at least one of the apparitions is actually her father -- and Jacob has an anger-management problem. Neither of these threads is resolved in more than the most perfunctory way possible.
From here it degenerates into somewhere closer to slasher territory, with the creature or creatures chasing the family around like Freddy Krueger popping in and out of dreams, and the family trying to fight back with Home Alone-style booby traps and hidden weaponry. I mean, previous swipes at the creatures have just passed harmlessly through them, so there's every reason in the world to expect that a knife will be able to stab them, right?
Even if you add science fiction elements to your story, changing the rules on a whim is bad form. If your creatures are intangible, passing through walls and immune to punches, then they cannot suddenly be blocked by doors or vulnerable to stabbing without some actual explanation. It's a rule that needs to be enshrined right up there with "stupid decisions characters make need more reason than keeping the story going". And for all the obvious hard work that went into making all three forms of these creatures work, they're not going to be actually scary without a better story to back them up.
Rating: 1 out of 5