How am I supposed to fight the headless bosses?

[DuelShockX]

I have a few pacifying agents and have the purple gourds but I barely do any damage to the thing and deflecting still deals damage to my health. Are there any other items that are needed for the headless enemies? I have 6 power and 15 vitality so I thought I'm ready to take them on with my items but I couldn't get through the first phase of the one near outskirts wall- stairway

[Razzberry91]

The headless bosses should be done later in the game (when you are stronger), but I think when you have 6 power you should be far enough.

Purple gourd and pacifying agent are indeed good to stand up to the terror build-up. However you also need to use "Divine Confetti" to give yourself a buff that lets you damage ghosts/spirits/demons. I would also recommend using "Ako's sugar" to give yourself an even higher damage buff.

[Xaphnir]

Divine confetti allows you to deflect their attacks without taking any damage or terror buildup, and is all but mandatory for the fight.

[Shizofrend98HR†]

You should fight em very last with divine conffetti. Purple umbrella, malcjotent whistle and all those other purple apparition damaging tools help too

[Alexoferith]

Leave the headless (there are 5 in total or 4 if you go for the Shura Ending, short ending), shichimen warriors (there are 3 in total or 2 if you go for the Shura Ending) after you have a decent collection of divine confetti. Confetti doesn't only buff up the damage but it allows you to parry the attacks from the Headless without suffering chip damage to your terror bar. Unless you are confident that you can parry PERFECTLY everytime, otherwise you will run out of the purple gourd and pacifying agent. I have seen someone defeating the headless without confetti but he or she parried perfectly everytime so he or she never suffer any chip damage.
Malcontent is only available once you defeated the apes twice and the shichimen warrior afterwards. You get the finger whistle from defeating Guardian Ape. Then you have to defeat the twin apes followed by the shichimen warrior occupying the same area as the twin apes. This warrior drops the upgrade part for the finger whistle thereby upgrading it to Malcontent.
The Malcontent can only be used THREE times, requiring 16 emblems (keep that in mind as you will have to restrain yourself using the flamethrower or mortal draw). Each time when used, it will stunt the headless, allowing you to put in 5 to 7 hits depending how quick your reaction are.
Don't mesh the attack button when attacking. Learn the timing of Sekiro's attack animation. So only press attack button at the end of each attack to get a chain of attack going. Aim for defeating the headless by breaking its posture if you can. Otherwise, prepare for a longer fight if going for health damage. Oh yes, the longer the fight, the more chance it will swing its head to shoot out those homing things, dealing terror damage. But you can avoid them by jumping sideway or dodging sideway as their "lock on" system seem to stop once you jump out of your original position.
There is one technique to defeat it making the fight jokingly simple but it needs a lot of practice and guts. When you get close to it, don't lock on to it. Run around it in order to get to its back and start swinging your sword. It will try to turn to face you in order to start its attacks. So, run to its back (you have to run, walk will not work). Hit 2 or 3 times. Do Not be greedy. All the time keep watching it to see if it is turning. If it starts to turn (it turns in walking pace), then you run to its back. Meanwhile, if you face yourself correctly, your swing will still hit it even if you are facing it squarely. I always panick towards the end and moved away... sigh..
When it does a swing attack (seemingly) by bending its body 90 degree and turn horizontally, from where you are, jump forward twice without running, then turn around, do a thrust attack by holding your attack button and then release. Follow this by 2 normal hits. You can then follow up by running to its back or use your Malcontent if you have it. You will find the fight shorten pretty much.
Oh yes, before starting the fight, use a confetti and an Ako sugar. This will buff up the damage you deal quite a bit. Again, ways to shorten the fight.
Hope these help. Have fun and good luck.

[David Benioff]

Do you have malcontent?
If so, the easiest method (essentially a cheese lol), buff with ako sugar + divine confetti. Then, aggro the headless in question, use the malcontent, then R1 spam until the effect wears off (he'll deflect you or stop looking like he's staggered - easy to tell). You can do this a total of 3 times, which should be enough to (almost) kill him. Easy money

[Zombiezzzz]

Divine confetti is a must have versus those bums