Muhammad ibn Hasan al-Mahdī (محمد بن الحسن المهدي), also known as Imam Zaman (Persian: امام زمان), is believed by Twelver Shī‘a Muslims to be the Mahdī, an eschatological redeemer of Islam and ultimate savior of humankind and the final Imām of the Twelve Imams who will emerge with Isa (Jesus Christ) in order to fulfill their mission of bringing peace and justice to the world. Twelver Shī‘a believe that al-Mahdī was born in 869 (15 Sha‘bān 255 AH) and assumed Imamate at 5 years of age following the killing of his father Hasan al-Askari.
Dajjal or Antichrist will be before the reappearance of Imam Al-Mahdi (AS) and he will be killed by Imam Al-Mahdi(AS) or by Prophet Easa (Jesus) by order of the Imam Al-Mahdi (AS).
Part of the responsibility of a leader is to know what is happening to his people. This is especially true for a divine leader (prophet, Imam).
Not all human beings have the qualities necessary to be good leaders. Some people have the social, intellectual, and emotional capacity, foresight, initiative, wisdom, and planning and communication skills to be great leaders. Most people do not. But that is ok, because we only need a handful of great leaders.
So, bearing this burden might be very difficult for the average person. However, the Imam is not an average person. Allah would not give the Imam this responsibility if he did not have the ability to bear it, as Allah says in the Qur'an that He does not burden with something beyond their capability. Because the Imam is at the highest level of spiritual perfection (as well as intellectual and emotional perfection), he has the capacity to handle many things that regular people cannot. Also, when people are truly at a high level of faith and have a deep and sincere connection with God, this enables them to bear things that other people cannot.
Still, of course, we should try our best to give the Imam a good report about our deeds and circumstances, and try to work as hard as we can to improve things around us!
We can not confirm nor totally deny this matter during the Ghaibah of the Imam (AS) as it is part of the personal life of Imam Al- Mahdi (AS) which is kept by Allah as secret and away from the public knowledge.
Some narrations mentioned his marriage and children but our leading scholars did not find such narrations authentic enough to establish a confirmed fact. Many leading scholars openly refused such narrations like Shaikh Al-Mufeed and Shaikh Al-Toosi and Shaikh Al-Bayadhi.
We have narrations refuting the claim of his marriage, such narrations are mentioned in many books like Ethbaat al-Wasiyyah by al-Mas'oodi, page 201, and Al-Ghaibah by Shaikh Al-Toosi, page 134, and Dala'il al-Imamah by Al-Tabari, page 130, and Al-Irshad by Shaikh Al-Mufeed, page 366 (Arabic edition).
We may advise Mo'mineen to leave this personal matter of the life of the Imam Al-Mahdi (AS) to the Imam (AS) himself when he will come back to the public life.
This Hadeeth ( Al-Mahdi's name is the same name of the Prophet and his Kunya is the same Kunya of the Prophet ) is narrated in many Shia and Sunni books. These are few Sunni books:
1. Sunan Al-Tirmithi, V. 3, P.343.
2. Al-Mo'jam al-Awsatt by al-Tabarani , V.8, P. 178.
3. Al-Mustadrak 'ala al-Saheehayn by al-Haakim al-Nisaboori .
And many others.
Imam Al-Mahdi (AS) is in occultation according to Allah's order, waiting for suitable time to come to the public life to establish the world government of peace and justice.
Allah (SWT) only knows when He will permit Imam Al-Mahdi (AS) to come to the public life to establish that great aim which is in fact the aim of all the Prophets and Infallible Imams.
Imam Al-Mahdi (AS) is living on this earth and he guides the scholars and helps people in the way that Allah (SWT) guides him. He is away from publicity and even those whom he helps do not know him. They will recognize him after his re appearance.
The evidence of the birth of any one is either witness from two trusted persons, or witness of trusted persons who saw him alive.
We have thousands of witnesses of trusted persons who witnessed his birth or / and saw Imam Al-Mahdi (AS).
Many Sunni scholars have also recorded his birth in their books like
1. Al-Dhahabi in Siyar A'lam al-Nubala 13: 119.
2. Mohammad Ibn Talha al-Shafi'ee in Matabilb al-Sa'ool .
3. Ibn al-Sabbagh al-Maliki in al-Fosool al-Muhimmah 237.
4. Sibt Ibn al-Jawzi in Tathkirat al-Khawaas.
5. Ibn Hajar al-Haythami in Al-Sawaa'eq.
6. Al-Shabraawi al-Shafi'ee in al-Et'haaf.
7. Al-Qundoozi al-Hanafi in Yanabee' al-Mawaddah .
8. Al-Shiblianji al-Shafi'ee in Noor al-Absaar.
9. Ibn Khallakaan in Wafayaat al-A'yaan .
10. Ibn Toloon and many others.
Imam Al-Mahdi (AS) is alive on this earth and he meets , guides and helps people. He knows them but they do not recognize him during the major occultation.
Few of the very sincere believers can recognize him after the meeting is over. The most sincere servants of Allah who are very rare, can recognize him during seeing him. Such sincere and humble servants never speak in public that they saw the Imam (AS).
This is a good question and one that doesn't have a clear answer.
One would assume that it would happen using modern weaponry (whatever that happens to be at the time), and there are some narrations suggesting the Dajjal might have some sort of modern machinery, and some of the signs of end times seem (God forbid) similar to the results of modern warfare. From this angle, the word "swords" in narrations could be taken as a figure of speech to represent weaponry.
However, it is also entirely possible that, at that time, something will have happened to make modern technology unworkable. (Some people have suggested a magnetic pole shift; one could also consider a massive solar flare, or really anything that would result in the destruction of the means of production or use of such items such as an environmental crisis.) This would also be concordant with the general description of chaos preceding the arrival of the Mahdi (A).
So, basically, there is no clear evidence either way; it is one of those things which we will have to wait and see. Of course the important thing is to be on the side of the Imam (A), regardless of what kind of technology is available.
The letter to Imam Al-Mahdi (AS) can be put in sea, river, well or any water. If you have no access to any water, then it can be buried.
There are many minor signs before the re appearance of Imam Al-Mahdi (AS) mentioned in many books, but no one can claim timing or expectations for any of the major signs because the major signs are definite signs before the Re appearance which is not known to any one except Allah (SWT).
This narration which you quoted (Hazrat Mahdi's father's name is Abdullah) is weak and not authentic even among Sunni scholars. The authentic Hadeeth stated : Al-Mahdi's name is like my name, and his Kunyah is like my Kuniyah). Liars added (His father's name is like my father's name.
Imam Al-Mahdi (AS) was born in Samarra in 266 Hijri. The birth of Imam Al-Mahdi (AS) has been mentioned by many Sunni leading scholars in their well known books.