13:1And he stood on the sand of the seashore. And I saw a beast coming up out of the sea, having ten horns and seven heads, and on his horns were ten diadems, and on his heads were blasphemous names.

And he stood on the sand of the seashore.

This sentence according to the best old manuscripts belongs with the last verse of the previous chapter. The devil is contemplating his next move.

And I saw a BEAST coming up out of the SEA,

While this may be a literal sea creature ugly as it is described, the most likely interpretation is that a demonic leader will come up from the "container of evil spirits", the SEA. The description of SEA in Revelation 17:15 would also indicate that the SEA means someone from among the world's nations.