Ha ha ha! I thought the Gumby short was great! I hadn't seen those Gumby "cartoons" since I was a kid and it was wonderful to see Mike and the 'Bots trash it. It was also funny to see Tom and Crow take the side of the robots. (Perfectly natural.)

I loved when they reacted in horror to the robots being chopped up and the head over the door.

The Gumby short "Robot Rumpus" just abounds with terrific riffs, especially with Crow and Tom witnessing atrocities comitted against their robot brethren. Besides the delight at watching Mike and the Bots tackle a good old Claymation short, the boys were in top form:

"Robot Rumps? Aw, I was hoping it'd be about robot rumps."
"One of my classmates died in the kiln today, Mother."
"Mrs. Gumby is stacked."
Gumby: "Look out the window, Mother."
Mike: "Pokey left a big surprise in your begonias!"
"Habitat against Humanity."
"It's a fair to partly-cottony day."
"I'll set you on Don Knotts strength."
"Don't, that's Wallace and Gromit's yard!"
"Mom threatened to make me into a bowl!"
"I'm going to glaze your backside, young man."
"Whoa, bad move. Robots do not fight clean. You know that, Mike."
"Oomph! Thank goodness for the internal genitalia!"
"Hey, you can throw things through Dad! I'm gonna get an anvil."
"When did Gumby get a Class F license?"

Upon seeing the mangled robot:
Tom: "Oh look at that robot! Oh that's disgusting!"

And upon seeing the robot head over the garage:
Tom: "AAIGH! They hung his head! Horrible! This is worse than Seven!"
Crow: "Now I'm ready for years of powerful Adlerian therapy, Mike."

You left out one of the best ones:

"That squares my breasts!"

This one is basically a live action Scooby Doo episode (evil character using fake supernatural stuff to scare someone away, so they can collect an inheritance).

There's a kernel of a good story here. The problem is that, even at minimum feature length, it's stretched out a bit too thin. It might have worked better as a Night Gallery episode.

Scooby Doo did this plot, over and over, in just half an hour.

I must respectfully disagree with your assessment. This movie can seen as sort of cross between Rebecca and Gaslight. Meanwhile, your average Scooby Doo villain typically enacts phony supernatural tomfoolery to conceal a covert activity, like an illegal sarsaparilla still or the like. But the biggest difference is that the supernatural proves to be real in Screaming Skull while in Scooby Doo all it takes is a single yank of the mask to reveal the spook as the fraud it is.

The husband in this movie was faking the supernatural to get to his wife's fortune.

Classic Scooby Doo plot.

Of course, the husband ends up dying, while the worst that happened to the Scooby villians was being hauled off to prison.