Complexius

Complexius is a pre-Hardmode boss, intended to be fought before or after the Eye of Cthulhu. It can only be summoned manually. It is summoned by using the Complexius Seed, which will spawn him a random distance away from you.

While Complexius is alive, the music Complexius will play.

Spawn
Complexius can be summoned manually by using a Complexius Seed in the Forest, and will not spawn automatically. The boss will despawn if you die. MrArtificial was here

Behavior
Complexius will usually rotate through his attacks, speeding up as he goes into his final phase. The first main "attack" is just him running at you. It is recommended the player is wearing Hermes Boots or one of it's upgrades, as he can quickly outpace you. Complexius will also spin above the player, and then slam down. When he does this, he can hover in the air for a short time before slamming down. You can take that time to quickly move out of the way. He will try to predict where you go, so if you see him start to spin, it can sometimes be a good idea to take a few steps backward. He will occasionally summon slow moving, spinning turtles. These are usually simple to deal with, but can be overwhelming, specifically in Normal Mode because they do not naturally despawn. In Expert mode however, they burst into very powerful rings of leaves. He will occasionally launch volleys of leaves, however these never prove to be much of a threat and are much less dangerous than the turtles.

When Complexius reaches 25% health, he enters his second phase. A ring of leaves grows around him. During the last quarter of his health, it is very advised to stay out of this ring. The damage from the Dryad's Bane debuff does not trigger immunity frames, which means it can remove your health very quickly if not taken care of.

Lore
A god once incredibly strong, weakened over time. Some folklore spread by Terrarians over the years are that the first life forms began on the back of this beast, small amoebas and bacteria, living in the moss. Over time, they began to evolve and spread off of him. However, as time went on, his body grew weaker. The Dryad race had just began to evolve, and Complexius was something of a father-figure to all of them, all of life. They watched over him, and weak as he was he was still a force to be reckoned with because of the Dryads lending their powers. But all good things must come to an end. A great war began, consisting of the Dryads and a great allpowerful being, Cthulhu. The Dryads were able to cripple Cthulhu greatly with their powers, but many lives were lost in that fight, and none were able to defend Complexius. Without the Dryad's powers, he grew old, and eventually dematerialized, into an everlasting slumber.