Monsters in the Bible
There is good biblical material to this effect, though I confess that the approach we're about to take in Monsters is likely very different than anything you might be expecting. Throughout the scriptures, diverse species of monsters appear—false gods (like Ba'al), cryptozoological fiends (like Leviathan), apocalyptic beasts (like the Beast from out of the Sea), and idols (like the Golden Calf)—and as they appear they strike terror in to the hearts of God's people.
Typically, we take this for granted: Of course Leviathan is scary, we think, he's a sea-born Chaos monster. But we never stop to consider whether or not these beasts are real or simply imagined. Ba'al, for example, was simply a stone statue. Asherah was contained in totem poles. No one has even seen a unicorn (mentioned, in Hebrew, in Job 39), nor was there any record of the Golden Calf laying waste to the Israelite's camp in the wilderness.
But, again, whether or not the object of our fears is real is less important than whether or not we're afraid.
The fear must be dealt with.
In most cases, I think we're safest to understand the descriptions of these creatures and cretins as either metaphorical depictions of evil personages (such as the dragon in Revelation, whom many understand to be a representation of the Roman emperor Nero, or possibly Satan), or imaginative descriptions of actual animals (the unicorn in Job 39, for example, bears a striking resemblance to a rhinoceros).
Whether or not these creatures were historical is less significant than the fact that the people within scripture were actually terrified of them. God's people were terrified of the false gods (even if they were just stone statues), Leviathan (even if it was just a crocodile), the Beast from out of the Earth (even if that was just a clever name for Diocletian), and the Ashtoreth poles.