Some monster weaknesses are well explained in various works.

Werewolves are burnt by the touch of silver. Probably because silver was often associated with moon.

Vampires can have this weakness too, or it could just be that they feel pain while touching it, or their wounds don't heal.

In some fantasy settings you can only kill an angel or a demigod with a golden weapon. But I have no idea why. Maybe because its used in temples or because it represents one of the capital sins - Greed. Heh... ironic.

And then there is the fext, a revenant from a 30-years war. impervious to all damage, except for glass bullets (or other odd items).

So how can I explain this weakness? (reasonably, without high doses of handwavium.) Real world mythology is as blurry as always and didn't care to provide an answer. Mythology stackexchange also did not provide an answer... yet.

I realize this could have so many different answers, so I will ask just in general

  • Why should a revenant/demon have a weakness against glass, or items not intended as weapons?

More about the fext:

It is a revenant, that came back, because he commited a bad deed and now has to redeem himself, or he has some unfinished business on this world, for example a revenge.

His skin is cold as ice and hard as rock. bullets fired at him either miss every time, or deflect off his skin, or are crushed on impact and then the fext throws it back in front of the shooter, while revealing his true nature. Sometimes a direct hit sends him to the ground, only for him to stand up again with the bullet in his hands. Sometimes depicted as cold and emotion less sometimes staring into their eyes tells you exactly what emotion they feel, sometimes this trick starts to freeze you from the inside. After the fext is put to rest, his body does not decompose, his skin will shrink and his muscles will dry or turn to dust. if a situation comes when he has to rise again, he will turn back to his original form.

This creature is partially created from the original slavic myth about revenants that are called "zmrzlík" - Cold one. Warriors that were called back from the dead, to help win the war. Cold to the touch and cold in their hearts, they were great tacticians. Their names later became interchangeable with fext.

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    $\begingroup$ Remember that most traditional weaknesses weren't explained. Why can vampires not cross over running water? None of the stories explained this. It just was. You're probably not going to explain how the fext is invulnerable, so you shouldn't explain why they are susceptible to glass either. $\endgroup$
    – sphennings
    Commented Dec 9, 2017 at 18:22
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    $\begingroup$ just like zombies, he is invulnerable, because he's dead, just in a different way than a zombie. And there is actually an explanation why vampires can not cross water, it is because springs were often blessed (even before christianity) and thus water created natural barriers against unholy creatures, such as vampires. $\endgroup$ Commented Dec 9, 2017 at 18:33
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    $\begingroup$ This is a classic "primarily opinion-based" question and I've voted to close it. No information about the fext exists and the OP does not add any insight. To avoid closure, the question should tell us about the fext. What is it like? Where does it get its energy? What are its motivations? What insight is there to its biology? At least we have some insight into glass bullets. If little or none of this is provided, then "because" is as good an answer as any, and that's off-topic. $\endgroup$
    – JBH
    Commented Dec 9, 2017 at 18:57
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    $\begingroup$ I'm voting to close this question as off-topic because, as you already mentioned in the question itself, this question has been posted on multiple sites of the network, i.a.: on the Mythology stack. PLEASE refrain from multi-posting questions, or at least wait until it gets either closed or you don't get the range of answers you desire before doing this. $\endgroup$
    – dot_Sp0T
    Commented Dec 9, 2017 at 19:35
  • $\begingroup$ In Mythology stack I asked about the origin of this weakness. and explanation in original folklore. (Because that's what its for.) While here I look for an explanation in fantasy. I will try to update the creatures' decription in 3 hours or so. $\endgroup$ Commented Dec 9, 2017 at 19:45

2 Answers 2


Glass is the most fragile of things. In the perverse backwards sense of the supernatural, the least can defeat the most.

Many supernatural creatures (especially, it seems to me, in Slavic / Norse type legends) incorporate aspects which are markedly in contrast to what one finds with ordinary beings. Or even the opposite. A vila will die if a single hair is plucked. A rusalka will tickle its victim to death. The giant monster Fenrir broke every chain which was tried until it was finally bound with a chain

wrought from the sound of a cat’s footsteps, the beard of a woman, the roots of mountains, the breath of a fish, and the spittle of a bird

I think also of how the invulnerable god Baldur was killed.


After these oaths were secured, the gods made a sport out of the situation. They threw sticks, rocks, and anything else on hand at Baldur, and everyone laughed as these things bounced off and left the shining god unharmed.

The wily and disloyal Loki sensed an opportunity for mischief.

In disguise, he went to Frigg and asked her, “Did all things swear oaths to spare Baldur from harm?” “Oh, yes,” the goddess replied, “everything except the mistletoe. But the mistletoe is so small and innocent a thing that I felt it superfluous to ask it for an oath. What harm could it do to my son?” Immediately upon hearing this, Loki departed, located the mistletoe, and brought it to where the gods were playing their new favorite game.

You know what happens next.

Glass is the most brittle of things. A bullet made of glass would shatter when fired - it is an impossible self-contradiction. Like a chain made of the sounds of a cat's footsteps. The impossible contradiction of a glass bullet is why it is the only thing that will work against a being like a Fext, which itself is an impossible contradiction.

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    $\begingroup$ Please don't answer questions that are obviously too broad and opinion based. It sets a bad example, especially since you're a high rep user. $\endgroup$
    – Aify
    Commented Dec 9, 2017 at 23:55

There is an old superstition that glass flows over long periods of time - which messes with the Fexts fluid transportation and thereby with the invincibility

According to Wikpedia in the past windows were created in a way that would leave on edge with a slightly different thickness than the rest. The ticker edge was mostly installed at the bottom of the window, which lead some people to believe that this old glass shows a "liquid" behaviour over a long period of time.

As we are talking about mythology here without any specific explanation as to the properties of this creature we can take this old superstition and use it in the context of this creature.

Let's assume that the normal invulnerability is caused by a special liquid, similar to blood, but different in its composition. Normally this special Fext-Blood would cause most wounds to close exceptionally fast, leaving them nearly invincible in the eyes of normal humans. But when this Fext-Blood comes into contact with glass it speeds up the liquidification of the glass, which would mix with the Fext-Blood and instead of increasing the new composition would decrease the rate of healing. Basically the liquid glass attacks the Fext from within.

The glass bullets were not the direct cause of death. It's the disabling of their regenerative abilities by an unknown reaction of glass, which combines with the blood of these creatures.


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