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Download raises either the Attack stat or Special Attack stat by one stage depending on the foe's lowest current defensive stat: it will raise Attack if the foe's current Defense is lower than its current Special Defense stat, otherwise it will raise Special Attack.
For determining which of the foe's defensive stat is lower, Download takes into account stat stages and the effect of Power Trick; however, it does not consider the effects of held items, Abilities such as Marvel Scale, or Wonder Room. In case of a tie between the foe's Defense and Special Defense, Download increases Special Attack.
During a Double or Triple Battle, Download will calculate the average Defense and Special Defense by adding the stats of all opposing Pokémon, and determine the lowest stat between both averages.
The Pokémon's Attack or Sp. Atk sometimes goes up when the Pokémon uses a move on an enemy. If the enemy's Defense is higher than its Sp. Def, Sp. Atk goes up, and if its Sp. Def is higher, Attack goes up!