PAIN

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First, you need to have purchased the Sore Spots level from the PSN store or the Pain store. Next, you need to purchase Santa from the same store. In PAIN reunion, you need to launch yourself at all the lockers on the upper level that have an X painted on them. Each contains an exploding crate which needs to blow up for the trophy to count. Once all of the lockers have exploded, the trophy will unlock. Some people have had trouble getting this trophy to unlock, but usually it's just a case of a crate not exploding or a locker getting missed. Keep trying and it'll work.