Is one who follows the whims of some online preachers, denying the cessation of Hellfire, and rejecting the return of the Messiah, the Mahdi, and the Antichrist, and slandering some of the Companions, and claiming the existence of fabrications in the books of Sahih, and denying the authoritative nature of Consensus (Ijma') and Sunnah, and disbelieving the fatwas of scholars, prioritizing reason over transmitted texts, to be considered an infidel?

Denying some established elements of the Sunnah, such as the Mahdi, Dajjal, and the Messiah, carries grave danger. Whoever denies the Sunnah commits an act of disbelief (kufr). Even if not for outright denial of the Sunnah, the perpetrator should be severely disciplined. As for the claim of the annihilation of Hellfire, it is a corrupt statement. Slandering the Companions, such as Mu'awiyah, is a sign of innovators. Cursing the Companions is forbidden, one of the most heinous prohibitions. Prioritizing intellect over transmitted texts (naql) is a grave error, especially if the person insists on disbelieving the transmitted texts after proof has been established against them.