Spirit is a creature type.
Details[]
Subtype[]
Spirit is a name for a collection of ethereal beings. Beyond that spirits can have any form or function.
History[]
Before Kamigawa block[]
In Alpha there were two spirits. Nether Shadow and Will-o'-the-Wisp. Both black creatures that don't die or don't stay dead.
After that came Arabian Nights. The set originally had no spirits but Dancing Scimitar had the ctype tacked on after R&D's big creature type change.
Antiquities only had Xenic Poltergeist.
Legends had a grand total of four spirits. Namely: Ghosts of the Damned, Lost Soul, Radjan Spirit and Thunder Spirit.
After that things subsided as The Dark only brought Banshee and Ghost Ship and Fallen Empires had no spirits at all.
From there on more and more spirits were made. In Ice Age a few creatures were given the spirit type even though they were more Elementals by flavor (Such as Flame Spirit) From there on every set had at least a few spirits with the notable exception of Nemesis. When the themes of sets became stronger it was obvious that there was less room for random creature types and there were a lot less per set. Invasion block has two spirits, one in Invasion and one in Apocalypse (set).
Odyssey block has just the cycle of phantom creatures in Judgment.
Legions had a Cycle called the muse cycle. These creatures are all spirits. Apart from that there is just Eternal Dragon in Scourge.
As the last silence before the storm there were three spirits thrown into Darksteel
Kamigawa block[]
Kamigawa block was centered around the Spirit creature type. There are 70 cards with the creature type spirit and 86 cards that mention the word spirit in Champions of Kamigawa alone. These numbers continued as 45 cards in Betrayers of Kamigawa and 49 cards in Saviors of Kamigawa. Also in Kamigawa block, Arcane spells were featured. These instants and sorceries were basically spirit instants. Soulshift was a mechanic in Kamigawa Block that let you bring back spirits from your graveyard to your hand.
This means that as of writing about half the spirit creatures in Magic are from the Kamigawa block.
After Kamigawa block[]
Since Wizards wanted to have more cross-overs in Standard constructed play Ravnica block had a minor spirit theme resulting in 34 new spirit cards.
Time Spiral block with its strong 'past' theme had 11 spirits, all of them references to older, existing spirits.
While Lorwyn block had no spirits, Shadowmoor block had 21 spirits, including 10 Spirit Avatars in the so-called Demigod cycle.
Shards of Alara has no spirits.
The Zendikar Block had 4 spirits, Bloodghast, Noble Vestige, Ruin Ghost and Soulbound Guardians.
Innistrad block[]
The Innistrad block, which has a night-type horror theme, has a focus on creatures of the night, each taking up an allied color pair. Spirits took up Blue-White in this block as ghosts and other apparitions. This added a total of 40 new Spirit cards, with additional non-spirit cards summoning 1/1 Spirit tokens, such as Lingering Souls and Doomed Traveller. With additional non-spirit and spirit cards providing additional support with Drogskol Captain acting as a Spirit Lord, and Angel of Flight Alabaster returning spirits from the graveyard.
Geist of Saint Traft was the legendary Spirit of the block.
After Innistrad block[]
The Return to Ravnica block had a few spirits like the original Ravnica block, adding 9 spirits including Legendary Spirit Obzedat Ghost Council.
The Theros block added 11 new Spirits, all of which were Enchantment Creatures showing off the focus of the block. Examples include Baleful Eidolon and Hopeful Eidolon.
The Khans of Tarkir block introduced 3 new spirits, Disowned Ancestor, Legendary spirit Anafenza, Kin-Tree Spirit and colorless non-artifact spirit, Scion of Ugin.
Battle for Zendikar had 1 spirit, Ghostly Sentinel.
Shadows over Innistrad, has introduced 17 new spirits with a subtheme however to a lesser extent than the original Innistrad.