Expelling Angels

Expelling angels is a spell that banished angels from Heaven.

Background
This spell was unknown to most angels. The only angel with initial knowledge of this was Metatron, the Scribe of God. Metatron convinced Castiel to perform the spell, under the notion that the spell was the set of trials that would lock the gates of Heaven to solve the problems of the angels. Wanting to atone for his sins and wanting to restore Heaven to its former peaceful state, Castiel agreed to the plan. Naomi caught wind of the spell and its near-completion. However, she was killed by the Scribe before she could properly recruit Castiel to stop the spell from being complete. When Castiel returned to Heaven, Metatron took Castiel's grace, thus completing the spell and banishing all angels save himself from Heaven. All angels, including imprisoned ones such as Gadreel were expelled, but many died in the fall, including Ezekiel.

According to the Angel Tablet, the spell is irreversible.

Procedure
The spell had three parts. It was essential to complete all three. However, the caster may vary among the three phases, as demonstrated by Castiel, who performed the first two, and Metatron, who completed the spell by performing the last phase.

Cut the Heart Out of a Nephilim
The first phase was to cut the heart out of a Nephilim. However, killing one without cutting the heart out appeared to have sufficed, as evidenced by Castiel stabbing the Nephilim's throat. Naomi described the process simply as "killing a Nephilim" when she read through Metatron's mind. According to Crowley's translation of the spell from the angel tablet, the heart of a Nephilim was one of the three ingredients, indicating that after Jane was killed, Castiel or Metatron cut out her heart.

Bow of a Cupid
The second phase was to secure a bow of a cupid. Castiel completed this phase by acquiring Gail's bow.

Removing the Grace of an Angel
The last phase was performed by Metatron, who removed Castiel's grace. Whether or not the grace required was that of the angel who performed the first two phases is unknown. Upon removal of the grace, the spell was completed and almost immediately sent the angels plummeting to the earth.

Appearances

 * Season 8
 * Clip Show  (first phase)
 * Sacrifice (second phase to completion)
 * ​Season 9
 * Heaven Can't Wait (mentioned and explained)