Pixie

Pixies belong to the surface Hallow, which means they cannot exist until you have broken into Hardmode and the Hallow has appeared. After that they need no trigger at all. Walk a hallowed hilltop at any hour and they turn up in numbers, glowing and flickering, and the light they give off usually announces them before you can make out the sprite.

Touching one is not what kills you. The contact effect is: either your movement drops away or your spells lock out entirely. Being silenced in the middle of a hallowed hillside with unicorns closing in is how a mage loses a trip that was never in doubt. Melee and ranged builds shrug most of it off, so the enemy feels wildly different depending on what you brought.

They look like they own the sky and they do not. A pixie can only hold itself a few tiles off the ground, so its practical reach is about the same as a zombie hopping at you. Ground level fights are the natural place to take them. What ruins the obvious counter is that they climb: a vertical wall is a ladder to them, so a pit dug across the path fills up and then empties itself over the lip. Plan for something that kills, not something that traps.

Every pixie leaves Pixie Dust, and that dust feeds so many early Hardmode recipes that almost every run ends up doing a session of this. The bobbing flight is exactly what makes the session awkward. Thin lava on the floor does nothing, since they hover over it. Trap lines are unreliable because a pixie is rarely at the height the trap fires at. What does work is anything that chases: short reach minions in particular, since they close on the target instead of waiting at a fixed line.

Once you have put down a mechanical boss the same kills start occasionally handing over an enchanted version of the dust as well, so a farming trip late in that stretch of the game pays better than one run the day you entered Hardmode.

World generation sometimes drops the hallow where the jungle already is, and you end up with no open hallowed surface to farm at all. Rather than hunting the map for a sliver of it, buy Hallowed Seeds from the Dryad and grow your own patch somewhere flat and convenient. A built biome spawns them the same as a natural one, and it has the side benefit of being shaped however you like. If you play across several worlds, the other option is simply to gather dust wherever the surface hallow came out properly.

• The design nods at the fairies of The Legend of Zelda, which are the same idea: a small ball of colored light with wings.
• The pet fairy that a Fairy Bell calls up looks close enough to be a relative, though that one follows you and lights your way instead of trying to silence you.
• Its idle chime is a long sample, so you sometimes hear one singing for a couple of seconds after you have already killed it.
• Both of its rare gadget drops, the Megaphone and the Fast Clock, can come off the same kill. They roll independently now, so it happens, just about never.