PAIN

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First, you need to have purchased the Sore Spots level from the PSN store or the Pain store. Next, start a two player game of PAINalympics either with two people or by yourself with two controllers. Select Anvil Toss as the first event. Launch with as little power as you can while still making it to the anvil, and immediately start ooching backwards. once you see that you have a negative score, you will have done it. You need to get a negative score on your first run for it to work. Thanks to Vyrastas for the following video: