Cornell comes upon a grand estate owned by the Oldrey family

During the course of the game, Cornell comes upon a grand estate owned by the Oldrey family: J.A. Oldrey, the master of the Villa, Mary, his wife, and Henry, their son. Gilles de Rais and Actrise have turned Oldrey Senior into a vampire. At Mary's request, Cornell guides Henry to safety. Later in life, Henry returns to Castlevania to save kidnapped children.

Throughout the game, Cornell encounters his rival and fellow man-beast, Ortega. Ortega has allied himself with Dracula to finally beat Cornell in combat, turning into a chimera like creature. They eventually battle near the end of the game, just before Cornell defeats Dracula and saves his sister Kanon Costumes
. He only accomplishes the latter by sacrificing his man-wolf powers. Unbeknownst to the hero, acquiring this power was the true aim of the dark forces, as it was the perfect sacrifice (not Ada, as Cornell had assumed) to resurrect Dracula at his full power.

Legacy of Darkness was a continuation of Konami's first attempt (Castlevania, also published in 1999) to create a 3D Castlevania Cosplay Costumes
. The game more fully realizes the game designers' vision. For example, Cornell was present in early development media and press information for Castlevania, but was ultimately removed before the game's release.

Legacy's primary focus is on a new story (a prequel to Carrie and Reinhardt's adventures) in which Cornell explores new levels, as well as redesigned levels from Castlevania 64. Levels from Castlevania 64 that have not been drastically changed (such as the Villa) are often navigated in a new or novel manner and feature different puzzles. Completing the game once unlocks Henry's quest, and he explores his own set of levels and new bosses, many are newly redesigned levels based on the levels of Castlevania 64 as well.

Carrie and Reinhardt's quests are a secondary focus (bonus features), that can only be unlocked after completing both Cornell and Henry's quests. Carrie and Reinhardt's quests lack the voice acting, some cutscenes and the original level designs present in Castlevania 64 (due to space concerns), instead adopting the new level designs (from Cornell and Henry's quests). Their quests also feature new bosses from Henry's quest, such as Medusa and the Queen of the Spider. They are also given new armor and weapon designs, though the original starting armor from Castlevania 64 can be unlocked during Henry's quest.

In Legacy control of the game's characters, camera, and frame-rate were streamlined. The game also supports the Nintendo 64's Expansion Pak add-on, which allows for an option in which textures are displayed in a higher resolution Kingdom Hearts Costumes
. However, this mode have some frame-rate issues. Legacy of Darkness also features several minor additions, such as an alternate costume for Cornell and new alternate costumes for Carrie and Reinhardt (their original costumes from Castlevania 64).