Dark Surge
Unleash the darkness and defeat the monsters released along it to obtain rewards.
Monsters infected by Dark Surge will appear when the stage has been completely flooded by the Dark Surge. Defeat them to absorb their Dark Energy and store it in the Container.
Click the Container when it's full to release the darkness and monsters. The first time you do this, you'll unlock a tier of rewards. After that, there's a chance to unlock bonus rewards each time. There are up to 4 tiers of rewards available. Every time you release the darkness, all the unlocked rewards will be carried by the monsters. Defeat them to obtain rewards.