Since they're sharing the same life bar, this will deal a great amount of damage. The entrance is also conveniently located under the Servants' Quarters bonfire so you can travel there as necessary. You want to run towards the top of the stairs and pick them off one by one, just be wary of the red spirit that invades your game. The giant bell above you will ring, letting you know that the cage in front of the mist door is now removed. Avoiding Ruin Sentinels means I am talking about Lost Bastille, an area early in the game. Doing so rewards you with a low level Heide Spear, but a moderate amount of souls. .
You can't access a certain endgame boss without the key you get from the Last Giant does that jump into the area still work? To overcome this, go back outside and face Lucatiels tower. Fighting them may be a little complicated, as they have a nasty attack - they drop to the ground and explode, dealing quite a lot of damage in the process. Quickly finish both of them off and have at the treasure in this room. On a ledge directly above you as you enter is a small mummy. You don't need to fight him if you don't want to - unless you attack him first, he will leave you alone. He uses two consecutive attacks that cover a circular area in front of him.
At the end of this ledge is a body with a Radiant Life Gem and a Large Titanite Shard to pick up. Take down the three guards inside, then climb up the ladder to the left to find a Green Blossom and a Large Soul of a Nameless Soldier. This can deal a large amount of damage if it doesn't just one shot kill you straight off. Another contains a ladder that leads up to a chest holding the Hush spell. Sprint and jump across the gap to the opposite rooftop.
Go back up the stairs to the third floor. Keep moving and avoid getting surrounded. You should spot a corpse holding an item over a small gap. The attack lasts quite a while and you will need to dodge multiple times if you were still in front of the sentinel when it activated the attack. After any of these attacks, you have time for at least one counter attack. Head up the stairs, watch out for the holes in the floor and defeat the Dark Spirit Bell Keeper. This makes an area you will reach shortly slightly easier.
If you are getting overwhelmed then run up the stairs, you can also jump down in front of the small archway if the top of the stairs become too heated. Go back upstairs and run through the bridge towards another tower. This can make killing them off difficult so use the terrain to your advantage as much as possible. If you're finding it difficult to reach the boss without getting invading try disconnecting your console beforehand this disables the online features allowing you to pass this area unhindered. After leaving the ship, go along the bridge, towards the shore and enter the building before you. Melee classes will just have to deal with the large mummy and dogs the old fashioned way. It is actualy an Old Bastille key used to open firepits before the Sinner boss.
Instead, take a right turn as soon as you go through the gate and kill the royal soldier around the corner guarding a corpse with a Life Gem on it. Backtrack along the ledge a little to find a slightly lower ledge to drop down to the top of the metal gate next to McDuff's workshop. Even worse if you have the bad fortune for them to use it on the small platform only triggered when the player and sentinel are at opposite ends of the platform. Now the room is free of enemies, head up to where the archer was to spot a clutter of barrels against the wall one is explosive. Be weary of a dog that will atack you from back.
You won't get many opportunities to attack the Lost Sinner, and when you can attack, it will only be with one or two hits before you need to block again. From where the dog appeared there should be a right turn nearby. Don't use this door unless you want to fall out and die. Head through the door and speak with the man sitting to the right. A thing to note here is you can use the window in the building opposite the corpse to shoot two royal soldiers with arrows or one with magic.
The Bastille Key will help you unlock the doors at the end of two staircases right near the entrance to the boss battle with the Lost Sinner. Head across to enter Belfry Luna. The only way to block the back stab is if you have that particular gargoyle targeted, if not then prepare to take a doozy of a hit. In this room you can also find a Club on a corpse and Priest's Chime in a nearby chest. The trick is to roll out of the window onto that little wall.