Today I'm going to walk you through why 
Scarlet Rot is so good and how to utilize it in every run.
For this to be prominent in every run you will either need to spend 1 sovereign sigil to convert the shifting earth to rotted woods to guarantee rot every run or do what I did and painfully save and quit over and over again.
It is one of the best status effects in the game as it is applicable to every single nightlord so it will make killing them come a lot faster. The Class we are using is the executor because it has S scaling in Arcane making it so status' activates more often and does more damage.
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Executor
The Ultimate Scarlet Rot Build Guide
ExecutorCreator
Intro
Equipment Loadout
For weapons you want to search for anything with the Scarlet Rot effect on the ground from the bodies outside of the fort in the rotted woods. Be sure to kill the Lordsworn Captian as he will drop a blue weapon with a high chance of it being rot.
For additional rot and to make sure you get it off quicker you will need either 
Rot Grease or 
Rot Pot.
The tiering goes as follows:
Grey Rot Weapon - 18 Rot per hit.
Blue Rot Weapon - 23 Rot per hit.
Purple Rot Weapon - 30 Rot per hit.
Now the best of the best are the weapons that already have natural rot from base elden ring, weapons such as 
Rotten Greataxe, 
Rotten Crystal Spear, 
Rotten Crystal Sword, 
Rotten Battle Hammer & 
Antspur Rapier. These are all amazing and don't need the added rot.
For Relics you'll want ones that give Attack power up when facing scarlet rot-afflicted enemy or anything that gives you Arcane for quicker procs.
Scarlet Rot
Rot GreaseConsumables
Rot PotConsumables
Rotten GreataxeColossal Weapon • Lvl Required 3
Rotten Crystal SpearSpear • Lvl Required 3
Rotten Crystal SwordStraight Sword • Lvl Required 3
Rotten Battle HammerGreat Hammer • Lvl Required 3
Antspur RapierThrusting Sword • Lvl Required 7
Game Plan and Pathing
Day 1
You drop in and immediately find the nearest Spectral Hawk to take you down to the rotted woods this is where you'll be obtaining your weapon as well as your consumables. While you're down here be sure to pick up the favor of the woods. There are plenty of scarabs here as well so if you have time grab some talismans. You can leave once you get the rot weapon as the circle will be shrinking fast, play the rest of day 1 out how you normally would, taking out easier bosses, collecting sacred tears.
Day 2
You will want to make your way back to the rotted woods as there are tons of bosses there that give good rewards, you will spend basically all day just farming away at the bosses within, they're all able to get rot and because they're so close you'll be able to get level 15 in no time.
Day 3
Now it's time for the nightlord, they ALL get rot so you don't have to worry about which one you're going for if you're in solo be sure to pick up your wending grace from the shop but these fights should play out as normal with rot doing a good chunk of their HP passively as you're fighting, it honestly makes it so much easier.
Additional Tips
If you want maximum rot be sure to grab a bunch of the 
Small Pouches as they will allow you to carry more rot consumables making sure the bosses will always have rot.
