Mummy

Mummies are Hardmode desert enemies that walk at you like zombies. No ranged attack, no clever movement, just a body coming toward you and a debuff on contact.

The spawn condition is looser than the biome name suggests. They do not need a desert and they do not need the surface. What they need is the right sand block to stand on, which means a strip of it underground, in a cave, or in the corner of your own base will start producing them. Worth knowing before you decorate with sand.

Which one you meet is decided by the sand. Plain sand gives the standard Mummy. Ebonsand gives the Dark Mummy, Crimsand the Blood Mummy, and Pearlsand the Light Mummy. Blood Mummies took over the Crimson slot in 1.4, leaving Dark Mummies as a Corruption exclusive.

• The standard one slows you. On its own that is survivable, but slowed in an open desert with more of them closing in is how it kills.
• Light Mummies confuse, which inverts your controls. Next to a cliff or a lava pool that is far worse than the hit itself.
• Dark and Blood Mummies silence and blind. Silence shuts a mage down completely, blindness hides the room, and both of these are already faster than the other two before anything else happens.
• Every mummy roughly doubles its walking speed once you take it below half health. Chipping away at one from a distance hands you a faster enemy, so either commit to the kill or keep well clear from the start.

Since the sand is the only requirement, there is no reason to travel. A one block high run of the sand you want, laid somewhere spawns are allowed, produces the variant you want on demand, which is the sane way to collect evil or hallowed shards and the Blindfold or Megaphone off the darker two. Those two drops are independent now, so a single kill can produce both, rarely.

One bit of pedantry: real Egyptian mummies were wrapped with the hands at the sides and the feet bound together. Terraria's, like nearly every fictional mummy, are left loose enough to walk.