Cthulhu Craze

Cthulhu's Craze is a War Mode event that can be summoned with the Lunatic Brain at night. It spawns in with the message: "Your mind goes mad!" Then the night sky will slowly transfer from black to greenish red. the moon sets on fire, and the level of light goes down about a bit lower than during a Solar Eclipse. The moon will burn as long as the event is occurring, and it is one of the best resources of light. The Demonic Monster and Shadow Cultist are Corruption worlds only monsters, while Blood Demons and Doom Cultist are Crimson-exclusive.

Monsters
NAME                    HP       DAMAGE        HOW COMMON          DESCRIPTION

Shoggoth               200        15                    common                    Furry lump with stalk eye and tentacles

Demonic Monster   555          50                 rare/medium              purple demon (in Corrupt worlds only)

Blood Demon          100          5                  common!!! demon covered with blood

Cthulhu's Spy           1567        75               rare!!! bloodshot eyeball with red iris

Doom Cultist            5000        156              rare rare rare!!! red and gray cultist (In Crimson worlds only)

Shadow Cultist          5000      150               see above                 purple and black cultist (In Corrupt worlds only)

Shine Cultist             5001        157            see above                   white and pink cultist

Cthulhu                     345,000   depends      boss                          Cthulhu

Drops
Suspicious Looking Fuzzball (1% drop from Shoggoth) summons Baby Shoggoth pet

Dark Gem (0.11 drop from Demonic Monster/Blood Demon) used to make Dark Amulet

Nightspark Staff (0.10% drop from Shadow Cultist) fires purple ball, 45 damage. takes 1/4 mana star

Fleshclaw Staff (0.10% drop from Doom Cultist) fires red ball, 50 damage. takes 1/2 mana star

Sparkle Staff (0.10 drop from Shine Cultist) fires pink ball, 49 damage. takes 1/3 mana star

See here for Cthulhu's Drops!