Symphony of the Night replaced Castlevania's linear whip-and-platformer structure with a non-linear RPG built around exploration, stats, and a sprawling interconnected castle that doubled in size mid-game.
Follows: Castlevania: Rondo of Blood
The term "Metroidvania" combines Symphony of the Night's series with Super Metroid to describe a genre defined by: an interconnected map, abilities that unlock previously inaccessible areas, and non-linear exploration within an open structure. Symphony is one of the two games the word names. Its castle is a single space rather than a series of stages — rooms connect to corridors that connect to other rooms, and progress comes from finding equipment or transformations that allow passage through previously blocked paths.
This structural approach had enormous influence. The genre it named became one of the dominant indie game categories of the 2010s, producing Hollow Knight, Ori and the Blind Forest, Dead Cells, and hundreds of others. Every one of them owes a structural debt to Symphony's castle design.
Reaching Richter Belmont, the apparent final boss, without preparation leads to a bad ending. The true path requires Alucard to wear the Holy Glasses during the fight, revealing that Richter is being controlled by the dark priest Shaft. Freeing Richter causes an inverted copy of the castle to appear, and the real ending lies at its end, in a final battle with Dracula.
Every room of the original castle is reflected upside down, with tougher enemies and a new set of bosses guarding the scattered remains of Dracula. The inverted castle was a revelation in 1997: it effectively doubled the game's scope at the moment most games would have ended, and set a precedent for hidden content that developers still reference.