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Boosts user's Defense two stages.
Defensive boosting moves are often looked down upon competitively, since very rarely do they help their user to escape the clutches of their common checks and counters, especially due to the existence of critical hits, and the boosts are lost as soon as one switches out, which is very likely for a defensive Pokemon. That's why you will most likely never see this move in a competitive environment, since it won't be very useful, especially if you have access to Reflect, which caps Defense at 1024 rather than 999.
Defense Curl is a Normal-type equivalent that boost user's Defense by just one stage.
Acid Armor is a Poison-type equivalent.
Reflect doubles the Defense stat up to 1024 Defense instead of 999.