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Ritual Summons usually require Tributes (from your hand or field) greater than or equal to, or sometimes strictly equal to, the Level of the Ritual Monster that is being Summoned. These Tributes are performed as part of the Ritual Spell Card's effect resolution, rather than as a cost. 
Performing a Ritual Summon
A player can Ritual Summon a Ritual Monster by activating a card or effect that performs a Ritual Summon (usually a Ritual Spell Card). When that effect resolves, the player must satisfy the requirements of the card/effect performing the Ritual Summon (usually Tributing monsters from their hand and/or field whose total Levels equal or exceed a specific value). After that, the player Summons the Ritual Monster from the hand (or other specified location) to an unoccupied Main Monster Zone in face-up Attack or Defense Position.
When a card or effect that Ritual Summons resolves, if the requirement cannot be met or the Ritual Monster cannot be Ritual Summoned, no Ritual Summon occurs, nor is any action taken for the Ritual Summon's requirement. For example, if a player cannot Special Summon when resolving a Ritual Spell that Tributes monsters, no monsters are Tributed.
Tributing monsters for a Ritual Summon
Most Ritual Spells require Tributing monsters whose total Levels equal or exceed the Level of the Ritual Monster, or whose total Levels exactly equal to the Level of the Ritual Monster. Monsters without Levels, such as Xyz Monsters and Link Monsters, cannot be used for a Ritual Summon that totals the Levels of the used monsters.
The player cannot use more monsters than necessary to perform a Ritual Summon. If any monster among the used monsters could be removed, but the Ritual Summon's requirement would still be met, then that monster cannot be used.
A player can activate a card or effect that Ritual Summons if all of their Main Monster Zones are used, but only if they Tribute one of their monsters on the field when that card or effect resolves (if all their Main Monster Zones are still occupied by that point).
Face-down monsters can be Tributed for a Ritual Summon, unless the card text specifies otherwise (such as "Forbidden Arts of the Gishki"). If a monster has an effect that allows it to be used as the entire monster requirement for the Ritual Summon (such as "Ritual Raven"), that effect can be applied when it is used for a Ritual Summon even if it is face-down. If the player can Tribute an opponent's face-down monster due to a card effect (such as "Soul Exchange"), it cannot be used for a Ritual Summon because its Level is unknown.
- While most cards that perform Ritual Summons are Ritual Spells, there are some other cards and effects that can perform Ritual Summons; for example, the Trap Card "Urgent Ritual Art", the Field Spell "Amorphous Persona", and the monster effect of the Pendulum Monster "Zefrasaber, Swordmaster of the Nekroz" can perform Ritual Summons.
- While most cards and effects Ritual Summon from the hand, some effects can Ritual Summon from the Graveyard, such as "Nekroz Cycle" and "Odd-Eyes Advent".
- While most Ritual Spell Cards require monsters to be Tributed or otherwise used, some Ritual Spell Cards have requirements that do not involve monsters, such as "Gishki Photomirror" which requires the player to pay LP.
- While most Ritual Spell Cards require the total Levels of the used monsters to meet a specific requirement, some Ritual Spells instead require the total ATK of the monsters to meet a specific requirement, such as "Meteonis Drytron". This allows Xyz and Link Monsters (who do not have Levels) to be used for a Ritual Summon, when they normally cannot be.
Ritual Summon support
- Some monsters have effects that allow them count as the entire Tribute for a Ritual Summon, regardless of their Level and the required Level; for example, "Ritual Raven" for DARK Ritual Monsters and "Gishki Shadow" for WATER Ritual Monsters.
- Some monsters (such as Djinn of Rituals monsters) have effects that allow them to be banished from the Graveyard instead of Tributing from the hand/field for a Ritual Summon.
Ritual Monster Summoning conditions
- A Ritual Monster cannot be Special Summoned from the Graveyard or while banished (except by Ritual Summon), unless it was originally Summoned by Ritual Summon.
In the original manga, besides the needed tributes, Ritual Summon also requires a proper monster to become the vessel for the Ritual Monster. For example, when Yugi used "Black Magic Ritual" and "Black Luster Ritual", he used "Gaia The Fierce Knight" and "Dark Magician" to summon "Black Luster Solider" and "Magician of Black Chaos", respectively. Similarly, Maximillion Pegasus used "Dark-Eyes Illusionist" to summon "Relinquished".
Yu-Gi-Oh! 5D's is the only Yu-Gi-Oh! anime series that did not feature any on-screen Ritual Summons, although one did appear in the Yu-Gi-Oh! 5D's manga. Prior to Yu-Gi-Oh! ARC-V, there were no common animation patterns for Ritual Summoning.
In Yu-Gi-Oh! ARC-V, when a Ritual Card is activated, the altar depicted on it appears on the field, and then the Tributed monsters turn into a number of flames (equal to their individual Levels) before positioning themselves on the altar. A pillar of fire rises from the altar and explodes in the sky, after which the Ritual Monster descends from the sky.
In Yu-Gi-Oh! VRAINS, a circle is formed and the Tributed monsters turn into a number of flames (equal to their individual Levels) and disintegrate into the sky, before entering the circle. Then an explosion occurs, and the Ritual Monster is finally created.
- "Individual Card Rulings [L-O]". UDE. Lich Lord, King of the Underworld. Archived from the original on 20 February 2009. Retrieved 12 December 2015.
- "Individual Card Rulings [L-O]". UDE. Mask of Restrict. Archived from the original on 20 February 2009. Retrieved 12 December 2015.
- "Individual Card Rulings [L-O]". UDE. Lightforce Sword. Archived from the original on 20 February 2009. Retrieved 12 December 2015.
- Jerome McHale (3 February 2010). "Absolute Powerforce Preview: Djinn Disserere of Rituals". Konami. Retrieved 12 December 2015.
When you Ritual Summon a monster, you need to Tribute monsters whose total Levels [sic] at least the Level of the monster you want to Summon, but you aren’t allowed to “overpay.” For example, if your Ritual monster [sic] is Level 7, you can Tribute a Level 5 and a Level 3 monster. You could not Tribute a third monster for that Ritual Summon.
- Scott Miller (23 February 2009). "How Ritual Summons Work". Konami. Retrieved 12 December 2015.
Some Ritual Spells let you go over that number, others require the Levels of the Tributes to exactly match the Level of the Ritual Monster. No matter what, if you have already selected enough monsters to fulfil [sic] the requirement, you can’t Tribute any extra ones.
- Scott Miller (6 January 2015). "Secrets of Eternity: Netherlord of the Flies". Konami. Retrieved 12 December 2015.
Remember, though, that you cannot overpay by Tributing more monsters than necessary to meet the “total Level 6 or more” requirement.
- "Individual Card Rulings [P-R]". UDE. Ritual Raven. Archived from the original on 20 February 2009. Retrieved 12 December 2015.
- "Individual Card Rulings [S-T]". UDE. Soul Exchange. Archived from the original on 20 February 2009. Retrieved 12 December 2015.
You can target a face-down monster, but you cannot Tribute it for a Ritual Summon or for “Metamorphosis” because you do not know its Level.
- "Ｑ＆Ａ » 手札やデッキから墓地へ送られた「トリシューラの影霊衣」を、「影霊衣の反魂術」によって墓地から特殊召喚できますか？" [Q&A » If "Nekroz of Trishula" is sent from the hand or Deck to the Graveyard, can it be Special Summoned from the Graveyard by "Nekroz Cycle"?] (in Japanese). Konami. 20 November 2014. Retrieved 3 April 2016.
- "Individual Card Rulings [D-E]". UDE. Dimension Fusion. Archived from the original on 18 February 2009. Retrieved 12 December 2015.
- "Individual Card Rulings [A-C]". UDE. Contract with the Abyss. Archived from the original on 17 February 2009. Retrieved 12 December 2015.
- "Individual Card Rulings [F-H]". UDE. Fulfillment of the Contract. Archived from the original on 26 February 2009. Retrieved 12 December 2015.
- Konami. Yu-Gi-Oh! Trading Card Game - Official Rulebook Version 6.0 (PDF). p. 15.
- "Ritual/Fusion Monsters vs. Legal Revival Target". 18 September 2007. Archived from the original on 2 November 2007. Retrieved 12 December 2015.
- Konami. Yu-Gi-Oh! Trading Card Game - Official Rulebook Version 5.0 (PDF). p. 13.