The Rotten boss in Dark Souls 2 is about as unpleasant as its name suggests, and when your opponent's not trying to slice your head off, it'll be coughing up vile poison to spit at you - charming. We've outlined all of the tactics you'll need to survive both phases of the fight in this next section of our Dark Souls 2 walkthrough.
How to kill the Rotten
You'll have to fight the environment as much as you fight the Rotten itself in this Dark Souls 2 boss fight. For a start, there are more than a few deadly fire pits scattered around the room, and if you touch one of them even a little bit, you'll lose a frightening chunk of your health bar. Stick around on any one of these areas for too long and you'll be toast before you know it.
You'll spend much of the battle against the Rotten locked onto the boss, and so it can be extremely easy to accidentally wander off into one of these pits. To make things a little easier on yourself, try to limit the fight to the centre of the battlefield, and circle-strafe your way around the fire in the middle. Do that, and you shouldn't run too much of a risk of wandering into another pile of fire.
As for the Rotten's attacks, there are only a few that you need to be aware of, and you'll make life much easier for yourself if you own a shield capable of absorbing 100 percent of the physical damage you block with it. With that said, you do run the risk of losing all of your stamina by spending too much time blocking the incoming damage.
"You'll make life much easier for yourself if you own a shield capable of absorbing 100 percent of the damage you block with it."
It's far better to dodge out of the way of these attacks if at all possible, and leave the shield for when you mess up your timing. For each dodge you manage to execute successfully, you'll be able to get in at least one whack against the boss - maybe two if your weapon speed is up to the job.
You can combine dodging and shielding if you find it a more comfortable approach - dodge the linear attacks that come your way, and block the big sweeping attacks that arc from left to right. The flip-side of this strategy is that'll you have less opportunities to dish out your own damage, and so will extend the length of the fight considerably. It's a balancing act which you'll need to perform for yourself.
Any time you back up too far from the Rotten, it'll use a variation of its single swipe attack, although the range can be quite deceiving, so be careful. The moment you see the Rotten lift its weapon up and over its head, get ready to block or dodge out of the way immediately. If the creature starts coughing up a hairball, back up to get out of the way of the deadly dark spit that's about to be thrown your way. Once this spitting attack has finished, get back in and continue the fight as normal.
When the Rotten's been taken down to around 50%, it'll add two more tricks to its attacking pattern. The first is very similar to that long-range slice, but the attack now includes a dark mist that darts out from the weapon and towards you. It'll come at you in a straight line, and so is quite easy to dodge, but you must be on top of your timing to avoid it. Make sure you dodge to the left or the right as well - if you jump back, it will still reach you. Feeling really feisty? Consider staying right up close to the creature if your timing skills can handle the pressure. That way you'll avoid these ranged attacks altogether.
The second new attack takes the form of a dark fog that emanates from the creature's body - it'll telegraph this using the same sort of retching animation it used in the first phase. There's not much range to this attack thankfully, so just make sure you back up far enough when you see it coming and you'll be absolutely fine.
As soon as your opponent drops to the floor, run through the fire and grab the item on the other side of the room. You'll be given a Fire Seed as your reward for finishing up the Black Gulch section of the game.