In Guild Wars 2, just about every profession can be any class, as long as it’s setup with the right skills and weapons. Control in particular is when a profession has a skill set that focuses on buffing allies and debuffing enemies. [A list of all GW2 classes]
This class is usually best in groups, since the buffs are more useful the more people who get them. Having a good Control player in a large PvP fight can really turn the tides of the battle. Decreasing the enemies DPS and increasing allies can make a tremendous difference in a game like Guild Wars 2. [Guild Wars 2 main page]
Control focuses primarily on buffing, debuffing, slowing, speeding, basically any positive or negative status modifications to allies and enemies.
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