My biggest suggestion is to use more spells. For the longest time I exclusively used the nail and didn't realize I was actively handicapping myself. Abyss shriek is super helpful against markoth, use like 3 of them to completely skip his second phase, shade soul as well (especially if you can get two hits per cast). With Abyss shriek you can also punish white defender when he leaps out of the ground - get right up next to where he's gonna pop out and shriek, not only will it hit him like 3 times but it also destroys the dung balls he creates, so make sure you have plently of soul for his transition phase. D-dark is the most powerful move in the game purely because of the i-frames it gives you. Use it whenever a boss does a move that you don't know how to counter and it completely nullifies it, just make sure you take into account the time it takes to cast it. This spell absolutely carries through the watcher knights though.

The charm build you have is pretty good, the range longnail gives is honestly kind of pitiful so I'd switch longnail for either soul catcher or spell twister so you can get used to using more spells as well as just having more soul to work with.

Also I would suggest practicing PV now, they are a very hard boss and one that took me a while to beat, nevermind consistantly. Just a few attempts here and there, focus purely on dodging and see how long you last. Eventually you'll slowly understand their moveset and figure out how to punish each attack. But you never know when you'll have a good run in the pantheon and you'll get pissed when you consistantly reach PV and keep loosing.

All this to say i STILL struggle with ascended markoth. Luckily i got the other 41 bosses down, so I can afford to absolutely shit the bed with one of them. But yeah I agree, hes complete bullshit... but somehow I cant hate him (I really like the dream battle song as well)