The Forgotten One is a super-boss in the PS2 game, Castlevania: Lament of Innocence. He can be found in Walter Bernhard's castle downstairs in the Prison of Eternal Torture. To fight him, you will first need to get the Unlock Jewel from the Pagoda of the Mystic Moon. A man-made monster, eternally sealed away due to an enormous, uncontrollable power.
Leon will be fighting the lower body and organs first. This is the easiest stage in the fight. The lower body's primary attacks are having maggots lounge at Leon with a chance of inflicting the curse status and acidic blood gushing out on the area of the walkway that can inflict the poison status.
After fighting the lower torso, Leon will be fighting the Forgotten One's hand. The Forgotten One will attack by slamming his hand or fist down on the platform, let out poison blood and then slam his hand down, or swipe his hand across the platform.
Finally, Leon will be fighting the Forgotten One's head. The Forgotten One will let out a powerful roar, causing rocks to crash from above. He will also sweep out a powerful breath of fire across the stage. The only protection from his fire breath is hiding behind one of the rocks that crashed down, but if Leon is hiding behind a rock that has taken a lot of damage from the fire breath, the rock will explode and Leon will take an extensive amount of damage. After the Forgotten One is defeated, Leon is awarded the black gem.
- The Forgotten One is very similar to Beelzebub from Castlevania: Symphony of the Night.
- There is also a downloadable final boss called the Forgotten One in the revamped Lords of Shadow series, only sharing the name and looking nothing like the original timeline's counterpart.