Another one of the numerous mysteries in Revelation is what the beast is. The way to solve this lies in a few verses. One, it says that Satan will give the beast its power. The beast will also be cast down into the bottomless pit along with Satan and the False Prophet, so the beast will be an individual entity.
The beast is the Antichrist, as in a human being with the spirit of Satan inside him. He is also the rider of the white horse that went forth conquering in peace the world. Halfway through the tribulation, he will die. Three days later, he will be given back his life through Satan. Satan himself in the flesh will be upon Earth. Satan is the rider of the pale horse. His name is Death and Hell will follow him.
This is why there is a difference when they are put in the bottomless pit. Satan will be in the bottomless pit along with the False Prophet, and the human being who his soul possessed. When you read Revelation keeping the beast in mind as the Antichrist human, it will begin to make sense for you. This is one of those mysteries where thinking too hard can take you far away from solving it. I hope this solves this mystery in your eyes, to those who have willing eyes and ears.