Legion & Nuculais Optional Bosses - Castlevania: Curse of Darkness
Legion is one of the 2 optional bosses in Castlevania: Curse of Darkness; the other optional boss is Nuculais whom spawns immediately after your fight with Legion. You can find both of these bosses in the basement of Garibaldi Temple which you can only reach by using the Magic Circle ability that the Devil IDs get.
The fight against Legion will be the easier of the 2 fights since Legion doesn't even fight back. Essentially how this fight works is Legion is a giant mass of flesh that floats down from the ceiling and you have to run up the spiral staircase that's in the room and attack it to defeat it. While you're trying to attack Legion you'll have an army of zombie-like enemies that will come out and attack you by exploding next to you.
You'll need to be extremely careful around the zombie enemies during this part because they'll each deal a significant amount of damage to you if they explode next to you. Each hit will be about 150 - 200 damage depending on what level your character is and what stats you have.
Once you destroy the massive hunk of flesh protecting Legion all that's left will be a small floating ball with some "netting" around it. Also, you may notice at this time that Legion has a single point of health left too - all that's left is for you to jump into the middle of this arena and attack it one last time to trigger the next boss fight against Nuculais.
Nuculais will be a significantly harder boss fight than against Legion and if you're not prepared he could very easily defeat you. If you want to make this fight a lot easier I would recommend weapons such as 7 Bladed Sword or Death's Scythe as both of them will deal Dark Damage which Nuculais is weak to.
I'd also recommend using a Battle Type ID such as Corpsey for the duration of this fight. Nuculais will often go after your ID instead of you and with an ID like Corpsey you'll be able to use Bone Storm to make him immune to all damage during the ability. This will give you a lot of free time to attack Nuculais as he attacks your ID in vain.
The most annoying ability that Nuculais will use is his lava teleportation skill. Sometimes he will create a big pool of lava that he jumps inside of and then he'll reappear in another portion of the room. You can block the lava attack if you see it coming but it isn't always easy to see it coming.
Another annoying attack that Nuculais can do is his grab attack which you can not block, you can only dodge it with a roll or by jumping. Getting grabbed by him will end up costing you a couple hundred life so you'll definitely want to avoid it. Nuculais also has an ability where he conjures up a bunch of corpses that rotate around him and he throws them at you. Some of these can be blocked but you'll probably want to block and dodge them as there's too many to block all of them.
Once you deplete the entire blue bar of his health and get him to half health he'll start to dig in the ground; during this time you will be able to attack him freely without any fear of retaliation. I'd estimate you have about 10 seconds of free attacks during this time before he digs up a corpse and eats it. Once the corpse is consumed Nuculais will become massive and he'll become very hard to hit.
While Nuculais is massive each step he takes will create shockwaves and damage you if you are hit by it or fail to block it. He'll also jump up and do a massive ground stomp which you can only avoid by jumping. Summon either a Mage ID, Devil ID or a Bird ID since all of them can attack from ranged while Nuculais is massive. It's best to avoid him altogether on Hector during this period since trying to damage him is too risky.
If you'd like more information about this fight than I provided on this page check out the Nuculais Castlevania Wiki page for more information.