Revelation 9:17-19

 "And behold, I am coming quickly. 

Blessed is he who heeds the words of the prophecy of this book."     

Revelation 22:7  NASB

The horses and riders I saw in my vision looked like this: Their breastplates were fiery red, dark blue, and yellow as sulfur. The heads of the horses resembled heads of lions, and out of their mouths came fire, smoke and sulfur. A third of mankind was killed by the three plagues of fire, smoke and sulfur that came out of their mouths. The power of the horses was in their mouths and in their tails; for their tails were like snakes, having heads with which they inflict injury. 

The heads of the horses resembled heads of lions, and out of their mouths 
Revelation 11:5  If anyone wants to harm them (the two witnesses), fire comes from their mouths and devours their enemies. This is how anyone who wants to harm them must die.

came fire, smoke and sulfur 
Isaiah 30:33  Topheth (a place of burning outside of Jerusalem where children were sacrificed to Molek, the god of the Ammonites) has long been prepared; it has been made ready for the king (of Assyria). Its fire pit has been made deep and wide, with an abundance of fire and wood; the breath of the LORD, like a stream of burning sulfur, sets it ablaze. 
Ezekiel 38:22  " 'I will execute judgment on him (Gog) with plague and bloodshed; I will pour down torrents of rain, hailstones and burning sulfur on him and on his troops and on the many nations with him.' "
Revelation 14:9-10  A third angel followed them and said in a loud voice: "If anyone worships the beast and its image and receives its mark on their forehead or on their hand, they, too, will drink the wine of God's fury, which has been poured full strength into the cup of his wrath. They will be tormented with burning sulfur in the presence of the holy angels and of the Lamb."
Revelation 19:20  But the beast was captured, and with it the false prophet who had performed the signs on its behalf. With these signs he had deluded those who had received the mark of the beast and worshiped its image. The two of them were thrown alive into the fiery lake of burning sulfur.
Revelation 20:10  And the devil, who deceived them, was thrown into the lake of burning sulfur, where the beast and the false prophet had been thrown. They will be tormented day and night for ever and ever.
Revelation 21:8  "But the cowardly, the unbelieving, the vile, the murderers, the sexually immoral, those who practice magic arts, the idolaters and all liars--they will be consigned to the fiery lake of burning sulfur. This is the second death."

A third of mankind was killed 
Revelation 9:15  And the four angels who had been kept ready for this very hour and day and month and year were released to kill a third of mankind.

by the three plagues of fire, smoke and sulfur 
Revelation 9:17  The horses and riders I saw in my vision looked like this: Their breastplates were fiery red, dark blue, and yellow as sulfur. The heads of the horses resembled the heads of lions, and out of their mouths came fire, smoke and sulfur.

their tails were like snakes, having heads with which they inflict injury 
Revelation 12:9  That great dragon was hurled down--that ancient serpent called the devil, or Satan, who leads the whole world astray. He was hurled to the earth, and his angels with him.

(parentheses are mine)

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