Mourning Wood

None of this happens by itself. The tree only exists inside a Pumpkin Moon, which you start with the Pumpkin Moon Medallion after dark, and that medallion is gated behind Plantera. Once the moon is running the event climbs through waves, and the tree is not in the pool at the start. It joins partway in and keeps coming until dawn ends the event. There is no version of it outside the moon.

The Everscream is the same design on the Frost Moon.

It walks, and it cannot jump, so terrain alone will stall it. The tell is the pause. When it stops moving, one of two attacks is about to come out. The first is a flat volley of burning logs that passes straight through walls, which is why a sealed box is worse cover than open ground. The second is a spray of flaming globs that arc down, land, and keep burning on the floor for a few seconds, so the ground beneath it becomes somewhere you cannot stand.

Two habits matter beyond that. If it spawns inside terrain it drifts through blocks until it reaches open air, so a wall will not keep it out of your arena. And it speeds up as its health falls, so the last stretch is the fastest part of the fight, usually with several other things on screen.

The ground fire cannot cross water. Flood the arena so the tree is standing waist deep and half its offense stops functioning, while the log volley carries on unbothered. Aiming a North Pole above it works too, since the falling snow rains down through it while you stay off the log line.

Kills push the event score, and that is the reason to kill it at all. Loot chances scale with the wave, so one killed early gives close to nothing while one killed deep into the moon is where the Spooky Wood, the trophy and the rest turn up. Play the moon for the wave counter, not for easy early kills. Expert worlds give it an exclusive drop, the Witch's Broom, and master worlds add a relic plus a chance at the Hexxed Branch, which makes it the only enemy that can hand you two mounts from one death.

• The name is a pun, from the same family as the Golden Shower and Master Bait.
• Splinterlings are its children. It snaps cuttings off its own body and pushes them into the soil.
• Real Greek fire was a Byzantine naval weapon, and some accounts have it burning on water, which is backwards from how it works here.