Unicorns are mythical animals which often represent things such as grace, purity and light in works. Given this, anybody killing or otherwise harming a unicorn can be taken to an utterly repugnant character. This can often mean that they've crossed the Moral Event Horizon, but it doesn't have to. Often, the act of killing the unicorn will cause some curse to be placed upon the perpetrator. This is a common trope in works that feature unicorns, due to the fact that the symbolic significance of unicorns is widely understood, making it useful in establishing or reinforcing villainy in a character. Not to be confused with Dead Unicorn Trope. See also: Moral Event Horizon.
- In Legend, killing the last two unicorns that guard the power of light would allow the demon lord to roam the world free in darkness. Also, the Big Bad shows just how evil he is by ordering a unicorn's horn to be cut off, which causes the world to freeze over.
- Killing a unicorn is seen as a particularly heinous thing to do in Harry Potter; Firenze refers to it as a "monsterous thing". The only person known to have done it in the series is Voldemort/Quirrel, further emphasising this. Drinking unicorn blood can prolong one's life, but the drinker will be cursed from the moment the blood touches their lips for having slain "something so pure and defenceless".
- King Lir from The Last Unicorn captured all the unicorns (except one) with the Red Bull and drove them all into the sea, just because he could.
- Somewhat subverted in The Siege of Wonder by Mark S. Geston, where the Scientists only see the unicorn's destruction as a bad thing because of all the knowledge and power that are destroyed with it.
- Merlin had The Labyrinth of Gedref. Arthur killed a unicorn despite Merlin warning him not to, and Camelot was cursed. Arthur had to succeed at three tests to prove his worth in order to lift the curse. He almost failed, but passed when he attempted to drink the allegedly poisoned drink to save Merlin. In the end, he buried the unicorn horn and the unicorn came back to life.
- in the Dilbert strip, when he is assignrd to the Marketing department as a punishment, Dilbert discovers a group of unworldly Elf-like types who boast every Friday s unicorn barbecue day. (Naturally, the eternal loser Dilbert gets the bun with the horn in). But elsewhere in the Dilbert universe we are told Marketing is a place of great and terrible primal evil... (in other strips, Marketing and Sales conspire to make life Hell for engineers by selling things they haven't designed yet. Hell: Marketing sell thingds that haven't been invented yet and which are generally scinetifically impossible...).
- In Magic: The Gathering, the Feast of the Unicorn card depicts the head of a unicorn roasted with an apple in its mouth, with the flavour text "Could there be a fouler act? No doubt the baron knows of one."
- Dungeons & Dragons Forgotten Realms setting. In order to create the Tome of the Unicorn (which was made of metal plates), a wizard named Shoon killed 12 unicorns and bathed the plates in their blood. This was considered an especially evil act in a world where evil deeds are quite common.
- Killing a unicorn of your alignment in Nethack incurs a sizable penalty to your Luck Stat. Sacrificing a unicorn of your alignment (whether or not you killed it) is generally a good way to suffer Yet Another Stupid Death, by way of invoking your god's wrath. Possibly a Zig-Zag example, in that you incur no penalty for killing cross aligned unicorns (and are in fact rewarded).
- Justified in Overlord. The whole forest is tainted by evil and you can (and should) mercy-kill them.
- Averted in Tales of Symphonia, where, even though you have to kill a Unicorn to get its horn to heal someone, the unicorn reveals that its death just means a new unicorn will be born elsewhere, so there is no "curse," nor is it an evil act, to kill a unicorn for a greater good.
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