Everscream is a Hardmode mini-boss that only spawns during the Frost Moonevent. It fires pine needle projectiles and bouncing ornaments which fragment like Crystal Bullets.
When the Frost Moon event ends, all enemies will flee including the Everscream. Unlike other event mini-bosses such as Mothron, who are invincible when the solar eclipse event ends, Everscreams can still be harmed and killed after the event is over, showing little to no retaliation. This allows the player to easily defeat the Everscream if they are fast enough. This trait is shared by the Mourning Wood.
Tips
Note that most of the Everscream's attacks can easily be avoided by staying on platforms high enough above the ground, as the attacks have limited range. Attacking with any ranged or long-range melee weapon from there trivializes the fight.
Everscream is one of the few mini-bosses whose attacks can be shielded, as its ornament and pine needle attacks do not go through blocks.
Trivia
Everscream's pine needle attack is similar to the Razorpine that it drops.
"Everscream" is a portmanteau of "evergreen" and "scream".
Everscream can be considered the Frost Moon counterpart of Mourning Wood, a mini-boss spawning during the Pumpkin Moon event, as they share the same AI.
Everscream and the Dark Mage are the only event bosses that cannot drop a ranged weapon.