When Elsa sings for Dutch Day, the candles on her hat are half melted. In the next shot, the candles have only melted a tiny bit.
Victor raises Sparky onto the roof with a swing set he attached to the attic skylight. When he let the kites go on his roof in the same scene, the swing set is gone.
On the chalkboard the word "Life" above the drawing of Sparky disappears in a following scene.
While the Frankenstein family is having fondue, the fondue sticks appear and disappear from the pot.
During the baseball game, Victor loops Sparky's leash around the bleacher post into a knot and tugs on it. In the shot where Sparky is looking at Persephone moments later, the leash is no longer tied and just hung on the post.
During the classroom scene when Mr. Rzykruski is explaining the mechanics of lightning, his diagram shows positively charged clouds above the ground, which is shown as being negatively charged by electrons. The diagram should contain negatively charged clouds (containing a surplus of negatively charged electrons) over the ground which should not have any charge.