The most important thing you can do to prepare for the fight with the Smelter Demon is equip a shield that's capable of absorbing 100 percent damage. Next, equip as much light armour as you can, so that you can strafe around the Demon nice and nimbly. The attacks used by the Demon aren't particularly complicated, but you do need to be able to move quickly to avoid the worst of the monster's damage. As long as you can keep out of harm's way, this is actually a pretty easy fight.
How to kill the Smelter Demon
When the fight starts, the Demon only has a light coating of fire. If you stand right next to the creature, you'll take a little bit of fire damage, but it's nothing to be concerned about at this stage. Just be aware that after you've dealt a certain amount of damage against your opponent, it will pause and take the opportunity to ramp up the flames spread all over its body.
Maintain your position when this happens, even though the flames will dish out more damage and do so across a wider radius too. Keep whittling the health of the Demon down until it reaches around 50 percent, at which point it'll plunge its weapon into its body to set it alight.
What about the enemy's attacks? Throughout this boss encounter, the Demon will make use of a small arsenal of attacks. There's a triple-hit combo that's made out of two horizontal swipes, following by a vertical one that's either grounded or comes after a jump. The jumping version's tougher to avoid, and the boss may even launch a burst of flames after the jump.
"The bottom line is that as long as you successfully dodge the Demon's attacks, it'll die before you do."
That jump attack can also be used independently of the combo, and the flames won't always appear after it's used. It's best to assume that it always will though, so you're suitably prepared. If you're standing too near to the Demon when the flame burst comes, you're going to take a lot of damage. When the body flame gets more intense, so does the flame burst range. You need to be approximately halfway across the battle area to dodge it entirely.
If you maintain a moderate amount of distance between you and the Demon, it'll use a straight attack that breaks your guard. It doesn't follow up with any more damage though, so you've got enough time to recharge stamina. Once the boss has lit that sword, it'll fire flames straight towards you. You can avoid it by staying very close to the Demon, or darting left or right with sharp timing.
As for your own attacks, stay close to the Demon and circle around it quickly. If you're fast enough on your feet you can actually block the first swipe of the triple-hit combo, the second part of it will miss, and the third attack will sometimes not even happen at all. When the Demon pauses for a moment, get two or three of your own attacks in, depending on your attacking speed.
You'll get a decent chunk of damage in using this strategy, but also take a fair bit of damage yourself. It's a worthwhile balance, however. If you're worried about your health at any point, consider using your next attacking opportunity to quaff a potion instead. The bottom line is that as long as you successfully dodge the Demon's attacks, it'll die before you do.
You can find more of our Dark Souls 2 guide from the index page.