Zombie

Zombies use the plain fighter behavior: walk at you, jump gaps, climb platforms, hurt you on contact. That is the whole moveset. They appear on the surface once night falls, alongside Demon Eye swarms, and they are the reason the game expects you to have four walls and a door by your first evening. They also give up. A fighter that cannot find a route to you wanders off rather than milling around outside, and it does not treat a closed door as a blocked route.

An ordinary zombie bangs on a closed door and cannot open it. During a Blood Moon it can, and so can any Blood Zombie that spawns then. Spore Zombie and Maggot Zombie ignore the restriction entirely and open doors on any night at all. Armed ones can never touch a door.

Doors only swing inward for them, which is what every standard defense exploits.

• Put a platform, a beam or any piece of furniture directly inside the door and it physically cannot open.
• Set the door a block above the ground outside, or dig a trench two wide and two deep in front of it, so they have to jump at it and never get the interaction off.
• Hang two doors side by side. Your NPCs still walk through, and the second door blocks the first from swinging inward. This one fails if you leave the outer door open.
• Or just wall the doorway with solid blocks for the night and cut it back open in the morning.

Zombies roll a size on spawn. Large ones carry more health, hit harder, resist knockback and have more defense. Small ones are faster and their hitbox squeezes into a gap barely over one block tall, which matters if you were counting on a low tunnel to keep things out of your base.

In Expert some zombies spawn holding a severed arm. Instead of walking into you they stop short and swing it, which outranges what you expect from a contact enemy and hurts more when it lands. They can only do it with their feet on the ground, so anything that keeps them airborne shuts it down, and they cannot use doors at all. The Armed Zombie Statue produces the same enemy in any difficulty. The bald variant is the only one that never picks up an arm.

The cheapest answer on night one is a box: wall yourself in, leave one gap at knee height, and stab through it with a shortsword or shoot through it with a bow. A wooden sword swung on rhythm holds off one or two in Classic; the third gets past the swing and starts eating your health. Anything that hits several targets at once is worth more than raw damage here, so a spear, Shuriken or Throwing Knife all outperform their numbers. A shallow lava channel outside the door does the work for you overnight, and a spear or the Vilethorn covers a trap corridor.

At dawn they turn and run for the edge of the screen, then vanish once they are out of sight. They can still clip you on the way out if their exit is blocked, though the armed ones stop clawing.

Which zombie you meet depends on where you are standing. Rain puts raincoats on them, the Snow biome freezes them, a surface Glowing Mushroom patch grows Spore Zombies that open your doors at any hour, and a rare jungle spawn after dark is Doctor Bones. Graveyards produce Maggot and Moss Zombies. A Blood Moon adds Blood Zombies plus the uncommon Groom and Bride. Eyezor only turns up during a Solar Eclipse. Each variant carries its own banner, so a spot that mixes several of them is a slow banner farm rather than a fast one.