Medusa

Marble caves in hardmode, and nowhere else naturally. Only one can exist in the world at a time, so you are always dealing with a single one, though the hoplites sharing the biome are usually the reason a fight with her goes badly. A Lifeform Analyzer flags her, which is worth having on if you are mining through marble.

She also speeds up as she loses health, from a moderate walk at full health to something you cannot outrun by the time she is nearly dead. The fight gets harder the closer you are to winning it, which catches people who plan to back away and finish her at range.

Her attack turns you to stone. While it holds you cannot move and cannot use anything, and it damages you when it lands. That is unpleasant on its own, and it is not the part that kills.

Being petrified switches off whatever fall protection you are wearing, increases the damage a fall does, and lowers the height at which falling starts hurting at all. The classic death is being caught while crossing a shaft. You lock up, you drop, and you land as a statue with none of your usual mitigation. A hellevator you dug yourself will do it. So will the open drops in the underground jungle. Anywhere near marble, stop treating vertical space as safe, because at endgame the fall alone is enough.

It also drops you out of a grapple or off a minecart, which is another way to end up falling from somewhere you assumed was secure. The one thing you can still do while petrified is drink through quick heal, so keep a healing potion off cooldown when you are in marble.

The attack has two requirements and a tell. She needs a clear line to you through blocks, and she needs you facing her when the animation completes. Before it lands, her hair lashes out, a distinct sound plays and yellow particles appear, so there is a genuine window to react in. Turn around, or put a single tile between the two of you, and nothing happens at all.

The problem is that most weapons rotate your character toward whatever you are aiming at, which means fighting her the normal way is what gets you petrified. So the answer is specific: use things that hit while you are looking elsewhere. Yoyos are the standard pick and a longer string extends how far you can stand off. A steerable projectile, or anything that works around a corner, does the same job. Her own dropped head is a fitting answer to her, since it works while you stare in the opposite direction.

If you would rather solve the consequence than the cause, a Featherfall Potion or Djinn's Curse removes the fall damage half of the problem even while you are stoned, and that is most of what makes her lethal in the first place.

Medusa statues ignore the one at a time limit, so a wired statue produces as many as you can handle. World generation occasionally places one already connected to a working trap, which is how a pre hardmode player can run into her long before they should. Statue spawns give nothing but the banner, so a farm built on them is only good for that and for the bestiary.

• The whole biome is a Greek joke. Marble, medusa and hoplite are all Greek words, and the enemies sharing the caves come from the same mythology.
• Her banner does not show her at all. It shows a snake on a gold Greek pattern, and the hoplite banner does the same thing with a helmet.