It is the antichrist (dajjal) who will shed blood in the End Times. Hazrat Mahdi (as) will come to halt these rivers of bloodshed by the antichrist.

One of the most important pieces of information about Hazrat Mahdi
(as) that our Prophet (saas) gives in many of the hadiths isthe fact
that Hazrat Mahdi (as) will cause no blood to be spilled at any time
in his life. Indeed, our Prophet (saas) says of the age under the
spiritual leadership of Hazrat Mahdi (as) that "he will not wake a
sleeping person or even shed onedrop of blood ." (Ibn Hajar
al-Haythami, Al-Qawl al-Mukhtasar fi `Alamat al-Mahdi al-Muntadhar, p.
29)
Our Prophet (saas) expresses this as follows in another hadith:
In the time of [Hazrat Mahdi (as)] no one will be woken up from their
sleep OR HAVE A BLEEDINGNOSE. (Ibn Hajar al-Haythami, Al-Qawl
al-Mukhtasar fi `Alamat al-Mahdi al-Muntadhar, p. 44)
Not shedding blood is Allah's command to Hazrat Mahdi (as) by
revealing it to our Prophet (saas). It is therefore impossible for
Hazrat Mahdi (as) to employ any other meansthan love, affection,
compassion, friendship and brotherhood in causing the moral valuesof
Islam to rule the world. Because any other behavior would mean
violating Allah's commandment, may Allah forbid.
Hazrat Mahdi (as) is a person of love and affection. The intense love
and affection that Allah creates in Hazrat Mahdi's (as) soul and that
will have an impact across the whole world are expressed as follows in
hadiths:
Due to the blessings of Imam az-Zaman [Hazrat Mahdi (as)] people's
hearts will be filled with mutual love and unity. (Bihar al-Anwar,
vol. 53, p. 187; Mikyaal al-Makaarem, vol. 1, p. 52)
[In the time of Hazrat Mahdi (as)] LOVE AND KINDNESS WILL PERVADE ALL
THE NOOKS AND CORNERS OF THE EARTH . (Iqbaal al-A'maal, p. 507; Bihar
al-Anwar, vol. 21, p. 312)
Certain people and circles with ulterior motives who say that blood
will be shed in floods in the End Times have ascribed, in their own
eyes, such a task to Hazrat Mahdi (as) both out of lack of knowledgeof
the hadiths and also deliberate distortion, of those hadiths under the
influence of satan. It is true that there will be bloodshed in the End
Times, but it is the antichrist who will shed it in floods, not Hazrat
Mahdi (as). The antichristmeans blood and pus. The antichrist will
elevate hatred of Muslims to its highest level in the End Times.
Hewill imprison the whole of mankind, and especially the Muslim world,
within an oppressive system, the like of which has never been seen
before. Our Prophet (saas) also describes this climate that will
emerge in the End Times in the hadiths:
(At that time) There will be much corruption, disorder and rebellion,
and people will kill one another. People will taketheir own lives and
the world will be filled with sorrow . The accursed dajjal will appear
at sucha troubled time...(Ash-Sharani, Mukhtasar Tazkirah al-Qurtubi,
p. 482)
At a time when the world will be in utter confusion and disorder, when
murders and tribulation appears ... when roads will be cut, when some
attack some others... (Al-Muttaqi al-Hindi, Al-Burhan fi Alamat
al-Mahdi Akhir az-Zaman, p. 454)
Allah reveals to our Prophet (saas) that Hazrat Mahdi (as) will not
shed blood and our Prophet (saas) imparts this to Hazrat Mahdi
(as).Hazrat Mahdi (as) will abide by this command of Allah.
Allah reveals to our Prophet (saas) that Hazrat Mahdi (as) will not
shed blood and our Prophet (saas) imparts this to Hazrat Mahdi
(as).Hazrat Mahdi (as) will abide by this command of Allah.
From Mr. Adnan Oktar`s interview on Adıyaman Asu TV on 27 September, 2010
Allah will send Hazrat Mahdi (as) to halt the flow of blood. Hazrat
Mahdi (as) is "anti-blood." It is Hazrat Mahdi(as) who will completely
silence Darwinism and materialism, the religionof the movement of the
antichrist that incite violence and conflict, cause people to regard
one another as animals, and incite selfishness, cruelty and
ruthlessness. In doing this he will use science and philosophy and
silence the movement of the antichrist with its own weapons.
With the total silencing of the movement of the antichrist, love,
affection, compassion, peace, security, brotherhood and friendship
will replace conflict, war, fighting and anger. All weapons will be
eliminated in the time of Hazrat Mahdi (as), and the money spent on
the military willinstead be diverted to science, art, technology and
other activities that benefit mankind. Our Prophet (as) foretold these
delights in the time of Hazrat Mahdi (as)1400 years ago:
All grudges and mutual hatred will be removed… Earth will be filled
with peace, just as a vessel is filled with water; . There will also
be unity in religion and none other than Allah will be worshipped
anymore. The (competents of) battle will abandon its load (arms and
equipment) . (Sunan Ibn Majah, 10/334)
(The competents of) Warwill abandon its load (namely, arms and the
like)… All hostility and hatred vanish.(Al-Sharani, Mukhtasar Tazkirah
al-Qurtubi, p. 496)