play castlevania symphony of the night or any metroid game and you'll get an example

Metroidvania is a game genre, it has nothing to do with Megalovania the song. Metroidvanias are defined by their explorable world and their upgrades that let you explore more of said world. The name comes from the two genre-defining games, Metroid and Castlevania: Symphony of the Night (btw Megalovania is named after megalomania, which is an obsession with power and also the name of the boss theme for Live A Live. As I said, no relation to metroidvanias). For a more modern example of a metroidvania, I’d recommend looking at Hollow Knight.