In a nutshell...
Loch Ness monster is preferred over Loch Ness Monster, even if the latter is more commonly used elsewhere.
Since cryptids are animals, the 'suffix' of the vernacular names of cryptids, such as the Loch Ness monster, should not be capitalised - it should follow sentence case. If the vernacular name contains a location, the location should be capitalised as it is a proper noun.
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