Unused content (SSBU)
For a list of unused Spirit Battles in the game, see Unused content (SSBU)/Spirit Battles.
Although every spirit in the game is obtainable, there are many that can never be battled, as they do not appear on the Spirit Board and cannot be battled in any other context (such as World of Light). This is true of every spirit that is an enhanced form, as well as many that can only be obtained by summoning. Most of these spirits have default placeholder battle data, but some of them are modified from the placeholder data to varying degrees. This indicates that it may have been intended for these battles to be accessible before they were cut from the game.
In addition to spirits whose battles cannot be accessed, there is data for "dummy" battles as well. These battles were likely used for testing during development and were not intended to become complete, accessible battles in the game.
Artwork & Alternate costumes