|Japanese (base text)||
A Pendulum Monster (Japanese: ペンデュラムモンスター Pendyuramumonsutā, abbreviated
Like Normal and Effect Monsters, Pendulum Monsters can be Normal Summoned/Set, or be Special Summoned by other card effects. While not in a Pendulum Zone, it is treated as a Monster Card and its Monster Effect is active, but its Pendulum Effect is not.
While in the Pendulum Zone, it is treated as a Spell Card and not as a monster until it leaves the Pendulum Zone. After resolving, it will remain face-up as a Spell, and will continue to apply its Pendulum Effects, if any (its Monster Effects are not applied when it is a Spell). These effects are treated as Spell Effects. A Pendulum Monster cannot be Set in the Pendulum Zone. Although a Pendulum Monster is treated as a Spell Card at this time, it is not considered either a Normal, Continuous, Field, Equip, Quick-Play, or Ritual Spell Card. Unlike a Field Spell Card, you cannot place a new Pendulum Monster over an existing one in the Pendulum Zone and send the previous Pendulum Monster to the Graveyard by game mechanics. As long as there are open Pendulum Zones, there is no limit to the number of times a Pendulum Monster can be activated from the hand per turn.
Once per turn, during the Main Phase, while there are Pendulum Monsters in both Pendulum Zones, the turn player can perform a Pendulum Summon, using the Pendulum Monsters' Pendulum Scales to determine the Levels of the monsters that can be Summoned.
When a Pendulum Monster (even if it is face-down) would be sent from the field to the Graveyard, either as a Monster Card or Spell Card, it is placed face-up in the Extra Deck Zone instead. (Pendulum Monsters can cause the total size of the Extra Deck to be larger than would be allowed during Deck building.) If a Pendulum Monster is sent from the hand, Main Deck, or Extra Deck to the Graveyard; has its activation as a Spell Card or Summon negated; or is detached, it is sent to the Graveyard like normal (as it was not on the field at the time). If a card like "Macro Cosmos" or "Grave Protector" is applying, this will override the Pendulum Monster's ability to return to the Extra Deck. A Pendulum Monster in the Extra Deck Zone can be Summoned again by Pendulum Summon, as long as its Level is within the Scales.
As the Pendulum Effects and the Pendulum Scales take up the space where the Set Number would usually be placed, it is placed in the bottom left corner of the card instead, in the same line as the ATK/DEF values of the Pendulum Monster. The art frame of a Pendulum Monster is increased in size, to the same width as the Effect boxes, and the Pendulum Effect box is partially transparent, allowing the art to be seen beneath it.
Pendulum Monsters' main weakness is their hand advantage cost to place in the Pendulum Zone, causing them to be vulnerable to effects such as those of "Black Rose Dragon" and "Evilswarm Exciton Knight". These "nuke" effects will destroy Pendulum Monsters in the Pendulum Zones as well as any Pendulum Monsters on the field, which will shut down any deck that relies on Pendulum Summoning until new Pendulum Scales can be placed.
In the anime, Yuya's Pendulum Monsters were originally Effect Monsters, but they were transformed by the power of Yuya's pendant into their current state. Declan would later manufacture his own Pendulum Monster prototypes, though he considers them inferior to Yuya's in terms of energy output and they initially malfunctioned. When a Pendulum Monster is placed into a Pendulum Zone, it appears in a transparent column of blue light from a portal on the ground not dissimilar to the Summoning of monsters in Yu-Gi-Oh! 5D's.
In the anime, when a Duelist uses Pendulum Summoning to gather the materials required for a Fusion, Synchro, or Xyz Summon, it is referred to as performing a "Pendulum-Fusion/Synchro/Xyz Summon" respectively.
- YGOrganization - [OCG] Pendulum Summons, New Mechanics, and Arc-V News!
-  - [OCG] Points of Interest from the New Rulebook
- yugioh-card.com/en Learn How to Pendulum Summon Tutorial Video (English)