Nuculais is a giant of light, born in the core of the Legion. His body is still imperfect due to being born before it was fully formed. He's an optional powerful boss in Castlevania: Curse of Darkness and appears as Legion's second form at the lowest depths of Garibaldi Temple.
Nuculais is a gigantic humanoid whose body is composed almost solely of light. This makes him extremely resistant to Light-based attacks, but also weak to Dark-based ones. Due to his body not being fully formed, it lacks any facial features and his hands and feet haven't developed fingers yet. The cohesiveness which maintains his molecules together appears to be unstable, which allows him to stretch his limbs or grow to gargantuan proportions for brief periods of time. A more developed part of his body is his heart, which protrudes out of his chest along with some partially formed veins.
For the second battle, Legion will actually be in human form (somewhat) and will no longer be immobile. It's advisable to forge and bring a 7 Bladed Sword for this battle, as it's the only Dark element based weapon in the game and it can inflict heavy damage to Nuculais with just a few swings, much more than with its next upgrade, the Laser Blade. It's also possible, but harder, to forge Death's Scythe and inflict massive amounts of damage to the boss in just a few seconds.
It's a good idea to use an Innocent Devil as bait for this battle. Set one of your Battle-Type Innocent Devil's to "Guard" mode and the boss will, most of the time, go after it allowing you to attack him from behind.
This boss has several attacks, most of which can be blocked. He'll teleport around the room constantly by summoning and jumping into a big puddle of lava and then rising out from another puddle in another part of the room. The lava is blockable, but the irritating part about this move is the fact that it will sometimes catch you in the middle of an attack if you're not cautious while attacking him. If he jumps at any time, then get ready to guard or dodge.
His other moves are a blade strike (blockable), a grab in which his arm will stretch out toward you (this must be avoided by rolling), several punches (he usually chains about four punches together, they can be blocked) and a move in which he will summon a bunch of dead bodies and hurl them at you. When he summons these, block the first set he throws at you, roll and quickstep from the second set and, for the third set, block the first few bodies, then roll and quickstep to avoid the move completely.
He also can project a purple beam which must be avoided as well (roll or run constantly). If you have your Battle-Type Innocent Devil in "Guard" mode, step into his shield and it will protect you from the entire beam attack. Another useful strategy is to have a Mage-Type Innocent Devil set to block. Nuculais will aim below the Innocent Devil and, as long as you don't stand in the way, it won't hit either of you. Hit him sparingly throughout the battle and watch for his attacks. The only time in which you can usually perform a full combo safely is when he recovers from a physical attack (punch or blade strike).
Once he's down to his second bar, he'll start digging in the ground. Run up to him and perform full combos while he searches through the floor. He'll finally pull a dead body out of the ground and absorb it, causing him to grow to gigantic proportions. When he's like this, he'll have very few attacks, but he can be extremely hard to hit without getting damaged. Each step he takes creates a shockwave on the ground (these can be blocked). When he jumps, he'll create a gigantic shockwave that will reach further than usual (jump to avoid it). Summon an Innocent Devil with a strong projectile move and have it fire upon the boss. Eventually, he'll shrink back down to normal size and the fight will continue as normal until you defeat him.