Deadly Spheres are Hardmodeenemies that spawn during the Solar Eclipseevent, only after Plantera has been defeated. They fly randomly in the direction of the player until close, at which point they rapidly charge and attempt to remain on top of the player.
Deadly Spheres will move through blocks to get close to the player, but are unable to charge through them to attack players.
Due to the Sphere's high defense, Vampire Knives and Spectre Hood's self-healing effect may not work on them if the player does not have enough damage buffs; the attacks will not deal enough damage to give health back.
Since they cannot get close to the player if blocks are in their way, blocking them off is enough to avoid taking damage from them.
Due to the Deadly Spheres' small size, minions and homing weapons are most effective.
Deadly Spheres have one of the highest defense ratings out of any enemy in the game, making weapons that deal large amounts of damage particularly useful.
The Morning Star does full damage to the deadly sphere, bypassing all of its defense (although this may be a bug).
Deadly Spheres are a reference to the 1979 American science fantasy horror film Phantasm.
With 80 defense, it has the third highest defense of all non-boss, non-invincible enemies, topped only by the Sharkron and the Dungeon Guardian.
The Deadly Sphere has an unused form in the files.
The Bestiary entry for the Deadly Sphere: "By means unknown, this silvery metamorphic sphere levitates about on its own. It moves about quickly, often producing spikes."