Old Iron King
The Old Iron King is one of four mandatory bosses you must defeat as a pre-requisite to opening the gates of the Shrine of Winter. The path to the boss is dangerous and filled with numerous strong enemies, including Alonne Knights and Ironclad Soldiers. Iron Keep is a tedious area to fight through due to the sheer number of enemies blocking your passage to the boss arena. You might be tempted to rush through Iron Keep, running past most or all enemies. However, it is safest to clear a path to the boss rather than rushing past all enemies. Defeat most or all enemies on the way to the boss. Crystal Soul Spear should allow you to two-shot each Alonne Knight. Consume one or more Brightbugs as you proceed through the area, or use the Brightbug glitch to help you conserve your stock of Brightbugs.
Iron Keep
Speedrun through Iron Keep NG+7, Dark Souls 2 SotFS
Start from the Threshold Bridge bonfire. Attune Crystal Soul Spear and optionally Sunlight Blade. These two spells can help you to quickly dispatch of most enemies at Iron Keep. The defense buff from a Brightbug can help you to tank at least one hit. Defeat the very first Alonne Knight, run to the iron gate ahead, but do not open the gate. Instead, wait for a scripted NPC red phantom invasion, either Armorer Dennis or Fencer Sharron would invade. Sharron is the easier invader to deal with. Use the large opening near her spawn point to create some distance between Sharron and your character. Spam Crystal Soul Spear at her. Dennis is the more difficult invader to handle because he tends to cast sorcery that can two-shot you. Equip the Spell Quartz Ring+3 to boost your magic defense. Use a melee weapon that has a one-handed wide horizontal R1 swing and buff your weapon with Sunlight Blade. Stay close to Dennis and R1 him two or three times, then move away to regenerate your Stamina. Rinse and repeat until he is defeated. Carefully choose your opportunity to heal, otherwise Dennis would one-shot you with Soul Spear.
Open the iron gate. Enter the room a bit to trigger an Alonne Knight to approach you. Defeat the Alonne Knight and prepare to defeat a further Alonne Knight x 2 and a red phantom Alonne Knight Captain. Ascend two small flights of stairs to find an Alonne Knight to your right. Defeat this enemy and wait for an Alonne Knight to run at you from a distance. Defeat this enemy as well. Enter the area with a large lava pool in the ground. Be wary of the Alonne Knight who shoots great arrows at you. Use the various large pillars to block his arrows. Three Alonne Knights would rush at you, one after the other. Defeat them and then use Crystal Soul Spear against the archer on the iron bridge. Four Alonne Knight Captains should be visible from near the iron bridge where you defeated the Alonne Knight archer. Get rid of the Alonne Knight Captain to your left; use Crystal Soul Spear to reach him.
Pull a lever to lower one end of the iron bridge. Defeat the Alonne Knight at the far end of the bridge. Find a circular turnstile (aka an iron wheel) and interact with the contraption to extinguish the fire within the adjacent mound. To the right of the mound are an Alonne Knight and an Alonne Knight Captain. Use Crystal Soul Spear against both enemies and you should find an Alonne Knight rushing to the location where you defeated the Alonne Knight Captain. Defeat this third enemy as well. Open the door to the mound, but do not enter. Two red phantom Alonne Knight Captains are found within. Lock onto the Alonne Knight Captain to your left, perform two casts of Crystal Soul Spear, and run away to the other end of the narrow ledge. Wait for a red phantom Alonne Knight Captain to exit the mound and approach you. As soon as you see the enemy, lock onto him and spam Crystal Soul Spear. Find the remaining red phantom Alonne Knight Captain, lock onto him, and Spam Crystal Soul Spear until he is defeated. Climb the iron ladder and defeat the Alonne Knight Captain in the distance. The shiny behind the enemy contains an Old Radiant Lifegem.
Climb another ladder to find an Alonne Knight and an Ironclad Soldier in the distance. Defeat these enemies and enter the arena that has various hanging platforms. Be ready to fight the Alonne Knight who drops down near the lever. Lock onto the nearest Ironclad Soldier and cast Crystal Soul Spear to trigger the enemy to relocate to another hanging platform. Pull the lever to lower a platform, thus killing the Ironclad Soldier and an Alonne Knight. The lowering platform would reveal an Alonne Knight archer. Dispatch of this enemy. Then use a bow and arrows to lure the left-most Ironclad Soldier to your location, where you can engage in one-to-one combat. In the far distance, look for an Alonne Knight who stands with his back facing you. Use a bow and arrows to lure this enemy to your location where you can safely fight him. Now pull the lever to reveal the original hanging platform. Proceed to the Alonne Knight Captain in the distance and get rid of him. Make your way to the Ironclad Soldier to your right and fight him as well. You should be able to stand on a hanging platform, lock onto the Ironclad Soldier, and spam Crystal Soul Spear at him.
Enter the mist. Stand near the descending staircase, wait for an Alonne Knight to drop down and rush at you. Defeat this enemy, then find another Alonne Knight standing on an iron platform above you. Lock onto this enemy and defeat with Crystal Soul Spear. Descend the staircase and defeat the Ironclad Soldier. Pull the nearby lever to ready the guillotine. Run to the corner in the distance and lure out an Ironclad Soldier who is trying to ambush you. Dash back past the guillotine, lock onto the Ironclad Soldier, and spam Crystal Soul Spear. You might want to cast a Crystal Soul Spear, wait for the Ironclad Soldier to slam his hammer on the ground, move back, and cast Crystal Soul Spear. Proceed to the Eygil's Idol bonfire. A red phantom is guarding the ladder to the bonfire. Defeat this red phantom by spamming Crystal Soul Spear. Here is a cheese strategy. Move around the room and let the flame chip down the red phantom's HP. Light the Eygil's Idol bonfire and rest at the bonfire. Attune any spells you require for the upcoming boss fight. Crystal Soul Spear and Sunlight Blade are useful against the area boss. Pull the nearby lever to extinguish the various flame blowing from iron bull heads.
Old Iron King
Sorcerer versus Old Iron King NG+7, Dark Souls 2 SotFS
This boss is difficult due to one reason: the rather dangerous arena in which you fight him. Enter the arena, lock onto the boss, and spam Crystal Soul Spear at least three times. Then buff your melee weapon with Sunlight Blade and be prepared to fight the boss head-on. Occasionally the boss would bait with a slam of his right arm, followed by a slam of his left arm. Whenever you see him slam his right arm, wait a while to confirm whether or not he would slam his left arm as well. Get in one or more hits. The fire breath is easy to dodge, but you can use the location near the other fog wall to safely shield from the fire. Another attack to watch out for is the slam of both arms. Sometimes the boss would telegraph the attack by charging the arms with fire, then slam the arms. Run away as quickly as possible from the area-of-effect from the slam and the fire. Wait for the fire to subside, then run in for one or more hits. The final attack to be wary of is the charged laser from the right hand. Run or roll away from the location where the hand drops and move in to hit the boss a few times. Sorcery would allow you to quickly defeat the boss. Dodge the boss' attacks as per above, lock onto him, and spam Crystal Soul Spear.
Defeat the Old Iron King and warp back to Majula. Level up if you have sufficient souls, then purchase all Brightbug x 3 from Melentia.