Area: Lothric Castle How to get: When you take the elevator to the Lorian & Lothric boss fight, jump out of it as soon as it starts moving. Another platform will emerge from the basement. Ride it down. Turn around and you’ll see a corpse with an item – the slab you’re looking for.
Area: Archdragon Peak How to get: Next to the dragon corpse where you fight Havel. Spawn at the Great Belfry bonfire, then go down into the courtyard. Turn right and climb the stairs. Look for a ladder on the terrace and use it to get to the top. The slab will be on the ground by the dead dragon.
Area: Archdragon Peak How to get: After you beat the Nameless King, the clouds will disperse. You’ll see an item in the middle of the courtyard. It’s another titanite slab.