Ender pearl

In-Game:
An ender pearl is a small green-blue item bearing slight similarities to an eye, which sometimes drops when an enderman is slain. When held, the player can right-click to throw one, which has the same force and trajectory as a snowball. As soon as the pearl hits a block, the player will teleport to that location, taking a small amount of damage upon landing.

Theory:
Ender pearls are a type of telescopic lens imbued with magical energies. Endermen wear these on their eyes like contacts. When they look at a specific spot, they can focus these energies at the center of their vision to create a fold in space, which allows them to advance great distances at a single step. The rapid process momentarily leaves behind small holes in space. This explains their momentary disappearance, the fact that they always teleport the way they are looking, and the strange 'particles' they leave behind. (Note that the particles closely resemble the Void fog, which represents nothingness)

When a player manages to kill an enderman without damaging the pearl, it can be harvested for personal use. However, since the lens will not fit the smaller eyes of a human, it cannot be focused from a distance, and must be in contact with a surface to focus energy onto it. In order to change the focus speedily enough to fold space, the player must throw the pearl at high speed. Unfortunately, the pearl is constructed of a delicate, glasslike substance, so it shatters and can only be used once. When the player teleports, he arrives at the same moment the pearl hits the ground, and so takes damage from the flying shards.