Optional boss is finally down after 20-30 attempts on NG++. Talk about an annoying sponge of a boss with a pretty bullshit moveset. I may bitch, and whinge, and moan, and swear, and punch pillows, and bash my controller out of pure rage, but i've now proudly beat every single souls game bosses solo as an exclusively-melee halberd user. Don't let your dreams be dreams. Persevere skeletons, even when it may seem impossible.
I agree that Midir is one of the top 5 toughest bosses in the entire Soulsborne series, if only for the unpredictable moveset (Laurence is still worse). The key is to go double-handed, charge the head, and dodge towards its tail once you see it start to commence an attack: never go defensive or move backwards. Being under-leveled or playing fashion souls won't be your inhibitor in this fight, just getting lucky with your movements and the moveset it chooses to use. Keep at it. One of those bosses that seems impossible and bullshit, but can be manageable when you master your technique.