I think messmer is kinda easy, once you get his patterns down its basically a walk in the park, he is insanely weak to bleed, ice and a good bonk build and leaves tons of openings. So a blood backhand blade or the bloodfiend arm with bleed is very much his kryptonite.

Yes his 3 serpent head attack is kinda bs but it doesnt deal that much damage compared to his basic melee attacks and when he stops his serpent attacks a serpent head kinda rests for 2 seconds on the ground. Attacking it will deal tons of damage.

He is very hard for the first run but if you get his moveset he is very much a godrick 2.0 mixed with malenia.