Super Smash Bros. Ultimate's spirit system (a mechanic that allows you to "equip" various characters that mostly aren't in the game to buff your stats in certain modes) started off innocent enough. You basically just run through the World of Light campaign mode, do some secret areas, and you're good to go.
But over time Nintendo started adding in events, which increased the spirit count. The thing is: they never really provided a resource that helped completionists keep track of everything. Enter the unofficial Super Smash Bros. Ultimate Spirits Directory.
Lead by Andrew "Slowback1" Wobeck and a crew, the site showcases all (currently) 1303 spirits by the order they are listed in game. Other small features include the ability to warp to a random spirit and a quiz game (that has some kinks, like giving away answers occasionally) that spans the entire Nintendo-sphere and beyond.
Give it a shot if you're looking for that last spirit!
Directory [Smash Ultimate Spirits]