Enderman

Enderman ignores you until you give it a reason. Attack one, or put your crosshair on its face, and it shrieks, shakes and teleports straight to you. The look rule is the part that catches people out, and it has a clean counter: wear a carved pumpkin and you can stare at an Enderman all day.

What they carry is the reason to fight them anyway. Ender pearls throw as short-range teleports at a small cost in health, and blaze powder turns them into eyes of ender — the item that finds a stronghold and lights the portal at the bottom of it. The same eyes go into an ender chest, whose contents follow you between dimensions.

An enderman farm is the standard experience farm for exactly this reason. They spawn in crowds across the End's outer islands, and a ceiling low enough to keep their heads out still leaves their legs in reach, so a platform, a drop and a safe spot is the whole design; an endermite kept in a minecart gives the crowd something to converge on. In the Nether they gather in warped forests, and in the Overworld they appear wherever it is dark.

Water undoes all of it. Rain hurts them, standing water hurts them, and they teleport away from arrows, so an open fight is mostly watching one vanish. Endermen also pick up and set down blocks — dirt, gravel, flowers and a short list of others — which is why an old world slowly collects small holes and misplaced blocks near the surface.