PSoD, or Purple Screen of Death, allowed players to earn XP while offline, by disabling all features and starting a countdown that keeps counting while the player is offline. It was named after the "blue screen of death (BSoD)" that is displayed on Windows computers when it meets a critical error, forcing it to shut down.
Using this feature locked the game at Purple Screen of Death page until either the timer ran out or the player cancelled it (forfeiting all rewards).
The PSoD duration could be set in hours, up to 72 hours. A cost in Green Coins was displayed, and a reward of regular XP that was delivered after the PSoD duration expired. When the PSoD was used more frequently, an Exp Penalty increased, so using the PSoD had diminishing returns. This penalty decreased as you claim progress rewards, but the penalty didn't decrease below 0.01% times the number of hours for which the player has used PSoD (maximum penalty: 96%). The penalty was reset upon Ascension.
At low levels, the experience gain from PSoD was greater than what you would get from idling in the Battle Arena. This would quickly change, however, and it would become more efficient to idle if you were able to keep the game on. Moreover, idling would not invoke a green coin cost and would result in pixels, crafting material, and other types of currency. Therefore, PSoD had been great if you couldn't play the game, but inferior to idling if you could.
While running PSoD, you could turn Anti-Idle (and your computer) off. If the game was running when time ran out, you would be on the Dragon screen.
During PSoD, your Career, Blessings, Cards, 2x Quest Reward, Pet, and 1.5x Coin and EXP timer would freeze. However, your trees would die without being harvested and your Fishing Fatigue would reduce at its usual rate.