Gaffes

Morticia is stroking a bronze dragon while speaking with Gomez on the phone, yet near the end of the call, the dragon is gone from in front of her.

When Thing hands Mikey his hat, he is a left hand instead of his usual right.

When the plant captures Lafferty toward the end of the movie, it has just one limb around the villain's neck at first, but then in the next two shots of him gagging on the encircling leafy fronds and Uncle Fester freeing him while irritably scolding the plant ["How many times has Gomez told you not to play with strangers?"], there are two big limbs around the bad guy's neck, as if they're hands/arms that are trying to hug him [or choke him to death].

When Mikey bumps into the tombstone, it wobbles.

While being grappled by one of the plant's two forward-facing "arms", Parley Baer, the actor for Lafferty's character, can clearly be seen surreptitiously reaching his leather-gloved left hand over toward the plant's other, incorrectly-stationary "arm", as a hasty reminder to the film/animation crew that this other "arm" of the plant is supposed to be curling in on him, also.