When the 3 scientists drive to the mountains to search for the monster,they are in a gray sedan. When they stop to continue on foot,they are in a red convertible.
The horse Baragon kills is an obvious stiff puppet. Special effects director Eiji Tsuburaya recognized how fake the shot looked but chose not to redo it.
When Frankenstein notices the boar, the boar is clearly a model swinging its legs unconvincingly while rotating around on its support.
When Frankenstein tries to capture the wild boar, in the last shot of the boar running off, the tracks that the model is running on are visible.
Frankenstein keeps growing, but never outgrows his clothing.