Pendulum Monsters are a unique type of card in the Yu-Gi-Oh! trading card game. They can be used as both monsters and spell cards, allowing players to summon them in a flexible way. Each Pendulum Monster has a Pendulum Scale, which determines the range of levels for monsters that can be summoned from the hand or Extra Deck. To use Pendulum Monsters, players place them in the Pendulum Zone, which is a special area on the game board. When activated, they can help summon other monsters quickly, making them a strategic addition to many decks. This mechanic adds depth and variety to gameplay.