As you start with the latest expansion of the Bloodborne: The Old Hunters within a few hours of gameplay you meet the very first Boss Fight with Ludwig, the Holy Blade(provided you have progressed the right way). This Bloodborne: The Old Hunters Guide you can easily defeat the Boss Ludwig and also obtain the Legendary Holy Moonlight Sword after the Boss Fight.
Being you're very first Boss Fight you must be very excited to take him down as soon as possible and celebrate your first DCL victory, but you know how well Bloodborne game mechanics works and how powerful Boss Fight it is going to be. Without any further ado let's begin with the preparation for the first Boss fight.
Firstly know your enemy and his weakness, Ludwig is a Huge enemy with two phases each of it being very energetic and forceful. You need plenty of Blood Vials, Bolt Paper, and Hunter Bone(if you have it). Avoid taking Molotov as they do not damage much, if you want you can recruit one of your NPC which can help you with the fight with Ludwig. We had taken Valtr(NPC) in order to guide us with the Fight.
In the first few minutes of the battle, you must have noticed that his attacking techniques are similar to the once you had fought before like Cleric Beast, Vicar Amelia, Blood Starved Beast, etc. You feel you can take this guy down like the rest? Just don't underestimate him just because he is using the low-level attacks remember he is the Boss so he is definitely hiding his true power.
Hint: Avoid the wide sweeps and straight claw as they can easily take you off guard
Once you hit him twice or thrice he will bursts into pieces and then appear directly above you, so you must find a safe place(his hind legs) or simply keep running away from it. If you manage to get inside his targeted arm then you can perform a Visceral Attack which will provide him a good amount of damage. After his health bar is brought down to 50% he will go to Phase two which is more deadly and difficult to survive.
Ludwig has now understood your true power and takes himself to another level that is the Phase two and wields the Legendary Holy Moonlight Sword. No one knows how it came to him and now that he has the most powerful sword he will stand right in the center of the room instead to moving fast and attacking. If you move to close to him then he will start swinging his sword and slice you down and if you remain far ways from him then he will start shooting some kind of shockwave of Arcane energy which can be dodged.
Now that he is powerful as ever you need to plan something really quick before he takes you down to slice you into two with multiple quick swings of the sword. Also, the most dangerous attack in this phase is when light moving towards the blade which is above his hand and then performs a charged laser beam which can take 80% of your health and making it easy for Ludwig to kill you. If he uses this attack then be ready with your Blood Vials to regain your strength.
You will only have trouble if you don't have any NPC recruited or not have joined any League. If not hen also you can take him down nice and easy without any help by waiting for him to attack first and dodge it which will make him a little slow and then charge with your attacks and maximum hits. Once you have taken him Down by slicing his head, simply walk towards his head and interact with it to retrieve the Legendary Holy Moonlight Sword. Congratulation you have successfully taken the First Boss of the Old Hunter Down.