The ranks of Hazrat Mahdi (pbuh) and the Prophet Jesus (pbuh) will be very high because they will both come in the fiercest period of the End Times
Excerpt from Mr. Adnan Oktar's Live Interview on A9 TV dated September 10th, 2011
ADNAN OKTAR: Tamer asks; "Do the Shias believe that the Prophet Jesus (pbuh) will come as a- may Allah forbid- "ghost" as well?" No. The Prophet Jesus (pbuh) has been taken to a dimension, to a different dimension. He has been taken to the skies, to the Sight of Allah and he will be brought to this world from that dimension. That is expounded in the verse; it is explained in the verses of the Qur'an.
But Hazrat Mahdi (as) is a guide and servant. He is a guardian and servant sent to people by Allah. Just as the prophets that have come in the past as the Qur'an tells, just as the imams [religious leaders] who strove on the path of Allah have come and described; he is a blessed and immaculate servant among those. In the End Times, Allah sends Hazrat Mahdi (as), a saintly servant, as the last guide, the greatest guide of all times. Since he will come in the most intense period of the End Times his rank will be very high. Because he will have to strive against hypocrites on one side and against unbelievers and the system of the dajjal [anti-messiah] and the way of the sufyan; against Darwinism, materialism and against perverse movements and thoughts. The armies of satan and iblis [devil] will be directed against him in such disordered environment. Hypocrites and the lot of bigots will oppose him with all their might. That is why his rank will be very high. That is because it is very difficult. Bediuzzaman says, "he requires patience and fortitude. Otherwise he will remain barren and do harm." He will wage a powerful struggle since he is very patient and possesses great fortitude and faith. And Allah will open the way before him, insha'Allah.