Champions with aura effects provide a passive modifier to nearby units. Some auras buff allies, increasing their effectiveness in battle, while others debuff enemies, hindering their efforts on the battlefield. In almost all cases aura effects are unique, and cannot be stacked.
The exception to this rule is an aura provided by a purchased item. In the event that multiple champions are carrying an item with the same beneficial aura effect, each will receive two instances of the buff: one from the item they are carrying, and a second from the aura of their ally. No champion can ever receive more than two instances of a unique benevolent aura, regardless of how many nearby allies are providing the buff.