Mohg, the Omen is a boss NPC in Elden Ring. This boss fight is entirely optional but is required if you wish to obtain the Lord of the Frenzied Flame Ending. The reigning lord and hierarch of the ...

This is quite surprising because both Morgott and his twin Mohg were born as Omen Royalty ... after you take him below 60% HP and he will get significantly more aggressive with his attacks.

The Fingerprint Stone Shield can be found in the Cathedral of the Forsaken, which you'll unlock shortly after defeating Mohg, the Omen. If you need help on finding Mohg, please refer to its page.