What are the three unclean spirits like frogs?
The three unclean spirits like frogs are demonic spirits that come out of the mouths of the dragon (Satan), the beast (Antichrist), and the false prophet, sent to deceive the kings of the earth and gather them for the battle of Armageddon.
When the sixth angel pours out his vial upon the great river Euphrates, the water dries up to prepare the way for the kings of the east. At that same time, Revelation shows three unclean spirits, appearing like frogs, coming out of the mouths of the dragon, the beast, and the false prophet. Revelation 16:13 says, "And I saw three unclean spirits like frogs come out of the mouth of the dragon, and out of the mouth of the beast, and out of the mouth of the false prophet."
These three unclean spirits are identified as spirits of devils. Their work is to perform miracles that go forth to the kings of the earth and of the whole world, deceiving them so that they will be gathered together for the battle of that great day of God Almighty. This gathering of the deceived kings and their armies leads them to the place called in the Hebrew tongue Armageddon.
So the three unclean spirits like frogs represent a coordinated demonic effort, one voice coming from Satan himself, one from the Antichrist (the beast), and one from the false prophet, together forming a false trinity that works through deception and false signs to move the nations of the earth toward the final battle at Armageddon.
The scriptures
And the sixth angel poured out his vial upon the great river Euphrates; and the water thereof was dried up, that the way of the kings of the east might be prepared. And I saw three unclean spirits like frogs come out of the mouth of the dragon, and out of the mouth of the beast, and out of the mouth of the false prophet. For they are the spirits of devils, working miracles, which go forth unto the kings of the earth and of the whole world, to gather them to the battle of that great day of God Almighty. Behold, I come as a thief. Blessed is he that watcheth, and keepeth his garments, lest he walk naked, and they see his shame. And he gathered them together into a place called in the Hebrew tongue Armageddon.
From the books
This answer is drawn from these passages in the Mary Banks Faith Library.