What makes a monster terrifying?

[Harzel]

Monsters that become stronger, more vicious, or gain powers as they lose HP can be unnerving. AFAIK, the ones that explode on death are the only things like that in WoTC 5e materials, but you can certainly invent others. Damage shields can also create a conflict about when/how to inflict damage, although they are often just yet another reason to fight at range.

 

[generic]

Monsters that become stronger, more vicious, or gain powers as they lose HP can be unnerving. AFAIK, the ones that explode on death are the only things like that in WoTC 5e materials, but you can certainly invent others. Damage shields can also create a conflict about when/how to inflict damage, although they are often just yet another reason to fight at range.

Actually, The Angry from MToF is like this.

 

[Harzel]

Actually, The Angry from MToF is like this.

Ah, yes, you are right. I didn't remember that one. It is certainly possible that there are some others.

 

[Chaosmancer]

One thing I've found is one reason why I love Abominations.

Anything that doesn't want to kill you, it wants to infest you. It triggers something primal in the brain to realize that you are going to become an egg sack or something similiar for a horrid thing and even the possibility of it ends up with players going for the "burn everything and salt the ashes" approach.

In fact, any foe that can spread over time, making more of itself or making more minions if it is left unchecked is really terrifying, especially the closer it is to a location full of civilians the players know will just fuel this into a horror show. Some undead are really good for this, if you remove the limit that they can only have 5 or 7 of their minions.