The Super Mario RPG Remake brings back many beloved features from the original game, including the elusive secret boss, Culex. Like the original Super Mario RPG, Culex is not a required boss to beat; instead, it can be tracked down and unlocked optionally. However, tread carefully as Culex puts up a tougher fight than one might anticipate.
https://screenrant.com/super-mario-rpg-beat-culex-secret-boss/