Hazrat Mahdi (as) will have a very powerful body and voice; at the same time his words and speech will have a great impact across the world

Hazrat Reza (as) replied to Rayyan Ibn Salti when he asked whether he were the commander of the faithful: Yes, I am also the commander of the faithful. But I am not the commander of the faithful who will fill the world with justice. The promised Qaim [Hazrat Mahdi (as)] will arise advanced in age, but will have a youthful appearance. HE WILL BE SO POWERFUL THAT IF HE STRETCHES HIS HAND OUT TO THE LARGEST TREE IN THE WORLD HE WILL UPROOT IT AND CAST IT AWAY, AND IF HE SHOUTS AMONG THE MOUNTAINS, HARD ROCKS WILL TURN INTO POWDER.  He will have Moses’ (as) staff and Solomon’s (as) ring... Allah will keep him hidden from sight until He wills. He will then appear and will fill the world with justice where it was formerly filled with oppression.(Bihar al-Anwar, Vol. 52, p. 32; Al-Hurr al-Amili, Ithbat al-Hudat, Vol. 6, p. 19)