The Orphan of Kos is possibly the toughest boss in Bloodborne: The Old Hunters, rivaling Ludwig from the beginning. I recommend bringing a hard-hitting weapon like the Whirligig Saw or the Holy Moonlight Great Sword. You’ll want to deal as much damage as possible with each hit. You do not want this fight to go on longer than it has to. Like most other bosses in the game and the expansion, Orphan of Kos has two phases. In his first phase, Orphan will attempt to hit you with a large scythe-like tendon.
Most of Orphan’s attacks are designed to make you think that you should back away to avoid them. However, quickstepping away will usually put you right in range of all his hits, resulting in you taking tons of damage. Whenever he swings, it’s best to move towards him and quickstep to the left just before the strike comes down. His attacks during the first phase are also fairly easy to counter with your gun. If you’re good with parrying, you’ll have plenty of opportunities to go for visceral attacks. If you’re not good with parrying, do what I do and stay close to him and quickstep to your left each time he swings.
Orphan also has an overhead attack where he’ll lift up the tendon and swing directly down. This is the only time you should back away as it is very difficult to dodge this one. Occasionally, Orphan will pause and dig into his tendon. When he does this, one of two things will happen. He’ll either throw a blood pellet at you, which you can dodge easily by quickstepping to the side before it hits, or generate a circular wave of blood that’ll damage anyone caught within it. Basically, if you see him dig into the tendon, back away and watch what he does.
When you’ve gotten him down to half health, the fight changes drastically. His weapon becomes much larger, his attacks more wild and vicious, and he also becomes more agile. Orphan can also be parried during this second phase but I highly recommend you stick to dodging instead. Getting caught in one of Orphan’s combos could result in instant death if your vitality isn’t high enough. Try to stick close to his sides each whenever he’s attacking. You’ll have a very small window to attack each time he’s done with a combo. As usual, back away if you need to heal up.
Orphan of Kos will also jump into the air, causing you to lose your target lock. Whenever he does this, sprint around the map until you hear him land. Orphan will also occasionally stop in his tracks, allowing you to get some hits in. However, I recommend taking only two or three hits before you start rolling around the map. Whenever he stops, it means he’s about to unleash a devastating magic attack. Tracking bolt fields will appear randomly on the ground to damage you. No matter how fast you run or roll, it seems impossible not to get hit by at least one bolt field that knocks you on your back. Once you recover from the attack, quickly heal before you continue your assault. This magical attack is probably the most dangerous one you have to look out for.
The key to beating Orphan during the second phase is patience, and your full attention and concentration on his movements. As long as you’re constantly dodging around him, you should be able to avoid most of Orphan’s regular attacks. It’s only the jumps and the bolt fields that you have to look out for.