An Attribute is the little icon on the top right corner of a Monster card.
Monsters so far have only ever had one printed Attribute, however several cards like Light and Darkness Dragon have multiple attributes when face up on the field.
Also, there are many other attributes exclusive to certain video games. However, those video games do not follow the rules of a regular Yu-Gi-Oh duel. Video game attributes include Dream, Thunder, Shadow (which could be referred to as Dark) and Forest.
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