Yajuj and Majuj are two huge nations of the sons of Adam. They exist at present, and they are attempting on a daily basis to get out and attack people. For more, see the detailed answer.

According to authentic Hadiths, the Mahdi is a prophesied leader who will appear before the Day of Judgment. He will restore justice, unite the Muslim Ummah, and lead alongside Prophet Jesus. Many scholars affirm that the Hadiths about the Mahdi reach the level of Mutawatir, meaning they are widely reported and accepted.