The only one of those things that's real are giant squid. In fact there is even a deep ocean variant in the Antarctic ocean called colossal squid with is even bigger and meaner. Still nothing of what you might think as "unfathomed" scale. But big enough to battle with whales with those jagged swiveling hooks they've got on them. But I'd suggest you stay away from anything non-biblical, as it will likely mislead you off the track.
>>808199
KJV 1611 footnotes:
>Job 40:15 behemoth: Or, the elephant, as some think
Also in the same footnotes, unicorn = rhinocerots and leviathan is called mysteriously "the whirlpool"
>>807163
Nah it wouldn't be a dragon, because the word dragon is used interchangeably with serpent, adder, asp, etc.