Whats the self inflicted damage?

Fun fact: The Lost Sinner's Sword has a much faster parry animation than other Ultra Greatswords, comparable to that of Curved Greatswords -- making it a surprisingly effective weapon for parrying. This is most likely an international feature designed to represent the Sinner's unique parry attack against the player.

Bro i killed maughlin and the miracle woman in heide tower

With 0 sin, 40 DEX & 40 STR, an unupgraded Lost Sinner's Sword will have 184 base damage + 70 AR. Use this to make sure you haven't sinned. If the AR is lower than this, use Cromwell's first time free pardon to reset your sin level to 0. You only get one reset per character so be careful. Use a soul vessel if you need to adjust your DEX and STR stats.

Due to a glitch with the Iron Crown DLC, you will gain 1 point of sin without cause, however Cromwell will not recognize that you have sinned if this is the only sin point you've gained. Therefore, you will need to kill an NPC and then speak to Cromwell to reset you're sin level back down to 0. I highly recommend using this oppurtunity to complete the Pate and Creighton questline so you can gain both of their respective gears. Remember, even if you don't attack them during their fight, you will still gain 1 sin point if one of them dies. Thankfully, this glitch seems to only happen once per character file.

Hope this helps, friend.

So I was just testing something I think might help a lot of people. I was really unhappy when I saw that this sword scales with sin level because 1. I don't have a online membership so I can't removed sins and 2. That means I have to kill certain NPCs to get their gear. Long story short, I killed Pate for Creighton, Gren, Targray and invaded Licia. The sword dropped from 270 down to 234. (Unupgraded) I went to Cromwell to forgive my sins in a last hope it would change something and it actually did! The Sword went back to 270 dmg. I'm still confused about the sind mechanic but I thought Cromwell doesn't change your sin level. If anyone knows more about this please help me understanding it better. He also wanted 0 souls.

Broadsword is better

This sword hits like a truck if it is infused. Its light weight makes it a very nice main weapon for caster builds. The 2H power attack sends human size enemies flying. It is definetly worth trying out. Just do not kill any NPC or complete the quest with Pate and Creighton for it will raise your sin counter. Invading as a Red Phantom is also not an option.
For PvE its definetly a very good choice if you decide to play nice.

''You need to be killed by a Blue Sentinel to revert the downscale of the sin''
That's..not good news for me, I guess

Something I noticed about this weapon, the attack direction is controlled by your movement keys while you are locked on a target, so it operates ignoring the rules that most of the other weapons do. So if you are locked on a target and moving while attacking, it will change entire direction even if you are facing the target, it can be beneficial making you a bit unpredictable, but I found that it forces you to hold your ground much more.

If you have right stats this is perfect weapon for all three DLCs.
And yes - Sir Alonne too.
My stats are 53 STR and 53 DEX, VIT 47 (my carry weight with Royal Soldier's Ring +1 was around 38%) and 147 stamina...and this was most comfortable and quick win against him (just do one hit at a time)