Pendulum Monsters are a type of Monster Card. The first Pendulum was released in Starter Deck 2014. These are half Monster Cards and half Spell Cards.
In addition to being used as a Monster, a Pendulum Monster can also be activated from the hand as a Spell Card in a Pendulum Zone. If there are Pendulum Monsters in both Pendulum Zones, the player can perform a Pendulum Summon.
Pendulum Monsters can also be Tuner, Flip, Spirit, Normal, Effect, Fusion, and Synchro Monsters.
You can use a Pendulum Monster in two ways: either as a Monster Card by Summoning it, or as a Spell Card by activating it in the Pendulum Zone.
Placed on the Extra Deck
If a Pendulum Monster (even if 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 instead (this can cause the total size of the Extra Deck to exceed its limit of 15 cards). A Pendulum Monster is sent to the Graveyard like normal if it is sent from any location other than the field (including if it has its activation as a Spell Card or Summon negated). However, if the effect of a card like "Macro Cosmos" (which banishes cards which would be sent to the Graveyard) or "Grave Protector" (which shuffles monsters destroyed by battle into the Deck) is being applied, this will override the Pendulum Monster's ability to go to the Extra Deck.
Can't be sent to the Graveyard
Pendulum Monsters cannot be used to pay costs that require sending cards from the field to the Graveyard, as they would not be able to go to the Graveyard but would be placed in the Extra Deck instead; however, you can still Tribute them for costs.
Once per turn, during your Main Phase, while there are Pendulum Monsters in both your Pendulum Zones, you can perform a Pendulum Summon, Special Summoning multiple Monsters at once, using the Pendulum Monster’s Pendulum Scales to determine the Levels of the Monsters that can be Summoned. You can Summon Monsters with a level between the Pendulum Scales +-1. For Example if you have Pendulum Scale 1 and 10, you can Pendulum Summon Monsters with a Level from 2 to 9.
Non-Pendulum Monsters can also be Pendulum Summoned.
You can Summon Monsters from your hand and face-up Extra Deck. The Monsters from the Extra Deck have to be placed in the Extra Monster Zone or a Main Monster Zone a Link Monster Points to.