Hazrat Mahdi (as) is beautiful and radiant

He [Hazrat Mahdi (as)] is a beautiful young man, with a beautiful face. THE LIGHT OF HIS FACE rises to his head and the blackness of his hair. (Ibrahim Suleymanoglu, Mehdilik ve Imamiye [Mahdism and Imamate], p. 153; Iqdud Durar)

His face is RADIANT LIKE A SHINING STAR. (Ibn Hajar al-Haythami, Al-Qawl al-Mukhtasar fi `Alamat al-Mahdi al-Muntadhar, p. 33; Al-Muttaqi al-Hindi, Al-Burhan fi Alamat al-Mahdi Akhir az-Zaman, p. 22)
 
The Prophet (saas) said: “Hazrat Mahdi (as) is a man of 40 from my line.  His face is LIKE A STAR SHINING in the heavens.” (Ali Ibn Sultan Muhammad al-Qaari al-Harawi al-Hanafi, Risalat Mashrab al Vardi fi Mazhabi 'l Mahdi)
 
Hazrat Mahdi (as) is one of my children. His face is like a bright star. (Al-Uqayli, An-Najmu's-saqib fi Bayan Anna'l Mahdi min Awladi Ali b. Abu Talib Ale't-Tamam wa al-Qamal)
 
HE IS BEAUTIFUL OF FACE. THE LIGHT OF HIS COUNTENANCE BESTOWS GRANDEUR ON HIM. (Mari’ bin Yusuf Karami Hanbali, Fawaid Fawaid al-Fikr fil Mahdi al-Montazar)
 
He [Hazrat Mahdi (as)] is a young man of medium stature and A BEAUTIFUL FACE. ... THE LIGHT OF HIS FACE SHINES LIKE DAY over the blackness of his hair, beard and head, and gives him grandeur. (Al-Uqayli, An-Najmu's-saqib fi Bayan Anna'l Mahdi min Awladi Ali b. Abu Talib Ale't-Tamam wa al-Qamal)
 
It is related from Humran bin A'ayan that Imam Muhammad Baqir (as) was told: "... Hazrat Mahdi (as) will have a mark on his forehead, and HIS FACE WILL BE BEAUTIFUL." (Sheikh Muhammad ibn Ibrahim Numani, al-Ghaybah al-Numani, p. 253)