Spirits in Elden Ring are the fallen souls of the countless Enemies you defeat in the game. As the player progresses the game, they will be able to encounter certain Skills such as being able to summon the spirits of the fallen enemies, and upon calling their fallen souls, they can aid the player in combat. And apart from your Skills, Spells, Weapons, and Armor, the use of summoning Spirits is yet another combat feature that adds more options on how you want to appraoch certain situations. This feature where you can summon is an offline feature and is different to where you summon your friends or other playres which is available in Online co-op play. This page covers a list of all the Spirits featured in Elden Ring.
According to a (translated) interview with Hidetaka Miyazaki, "it is possible to summon spirits. You can summon these to become allies and fight with you when in the correct place." - the variation of Spirits of the enemies you defeat will vary here, you can summon the spirit of an enemy wielding a shield who can protect you from incoming attacks, how about an archer who can snipe your foes from afar, a fighter who wields a whip who can attack at mid-range or even a spirit who can cast magical spells. The possibility of summoning the spirits of the foes you encounter and defeat is seemingly countless.
Elden Ring Spirits
Spirits of the fallen enemies are summoned on the battlefield.
Spirits aiding the player in combat.
A whip-wielding spirit fighting an enemy in combat.