Mogh, Lord of Blood is one of the toughest bosses in the Elden Ring. You can find him in Siofra's River at Mohgwyn's Palace. It is worth trying to face him at the end of your progress. To get to him, you must find the Haligtree Secret Medallion. This boss fight is an optional and you don’t have to defeat him to progress in the game.
During the battle, Mohg's attacks will cause you bleeding effects if you don't dodge them.
The boss battle is divided into 2 phases:
The Mohg has a melee combo during which he will hit twice with his sword. Also, if you're in range of the boss's melee attacks, he'll cause an explosion around him from time to time and also use his deadly blood attack, you must get out to avoid bleeding.
You can use Mohg's Shackle to temporarily stun the him and deal heavy damage. Be careful because you will only have this possibility twice during the fight.
During phase 1 Mohg will also throw blood rings around your. This is a dangerous spell when you have 3 blood rings (nihil), you can use Purifying Crystal Tear (you can get this during Yura's quest line) to cover this attack.
Mohg still has a classic melee attack combo. Once in a while he will charge at you. Finally, it can fly away and cause a rain of blood.
Nothing special in this phase, take the time to move away when he is about to charge.