Why does God admit the One-Eyed Dajjal, Gog and Magog, and Iblis to Hellfire, even though they were created as disbelievers and different from humans to be a tribulation for them?

The questioner's distinction between the Dajjal, Gog and Magog, and Iblis, on one hand, and other accountable beings who possess choice and will, on the other, is an incorrect distinction. All those mentioned are accountable and possess choice and will. Iblis's accountability and choice are evident in the Qur'an, as in the Almighty's saying: " [Allah] said, "O Iblis, what prevented you from prostrating to that which I created with My two hands? Were you arrogant, or were you among the haughty?" He said, "I am better than him. You created me from fire and created him from clay." As for the Dajjal, and Gog and Magog, they are human beings from the Children of Adam and they possess free will.