When the two witnesses have finished their testimony, the beast that comes up from the Abyss will wage war with them, and will overpower and kill them.

Daniel 7:21
As I watched, this horn was waging war against the saints and prevailing against them,

Luke 8:31
And the demons kept begging Jesus not to order them to go into the Abyss.

Revelation 9:1
Then the fifth angel sounded his trumpet, and I saw a star that had fallen from heaven to earth, and it was given the key to the pit of the Abyss.

Revelation 12:17
And the dragon was enraged at the woman, and went to make war with the rest of her children, who keep the commandments of God and hold to the testimony of Jesus. And the dragon stood on the shore of the sea.

Revelation 13:1
Then I saw a beast with ten horns and seven heads rising out of the sea. There were ten royal crowns on its horns and blasphemous names on its heads.

Revelation 13:7
Then the beast was permitted to wage war against the saints and to conquer them, and it was given authority over every tribe and people and tongue and nation.

Revelation 17:8
The beast that you saw--it was, and now is no more, but is about to come up out of the Abyss and go to its destruction. And those who dwell on the earth whose names were not written in the Book of Life from the foundation of the world will marvel when they see the beast that was, and is not, and yet will be.

Revelation 19:19
Then I saw the beast and the kings of the earth with their armies assembled to wage war against the One seated on the horse, and against His army.

And when they shall have finished their testimony, the beast that ascends out of the bottomless pit shall make war against them, and shall overcome them, and kill them.