How do you instill fear into gamers?

[Bjarkmundur]

The way I see it, fantasy has shown us - using my trolls example - that everything varies. Some tales speak of trolls who live under a bridge, Tolkien taught us that trolls turn to stone if exposed to sunlight.

So I must ask, in the case that they've faced Gnolls from the MM, you wouldn't use the Gnoll Flind, Gnoll Flesh Gnawer, or Gnoll Withering later - all of which are found Volo's Guide, and while Gnolls, are quite different in terms of AC and things they can do... Just because they 'learned as common knowledge' what Monster Manual Gnolls are? Or would those be OK, just because they're in Volo's guide and not the DM's own creation? Trying to find the difference.

Yeah, you got me :S
After some amount of self-reflection, I realized my opinion comes from one bad session involving a "custom dragon" many years ago. I guess I'm just still bitter that for some of the other players that thing we fought was their first exposure to fighting a dragon as the hero of a story. I would've been OK with it if the novice DM at the time had some creative reasons for the changes he made, or a rich backstory or relevance to the plot. But no. It was awful, and it was terrible to see the creature that I usually spend MONTHS creating an aura of terror and mystery around to be introduced and dealt with within an hour. So, guess you can call it an illogical pet peeve?
I now know that it's unresonable and illogical, and I'll try to remember that in the future. More good things come out of creatively changing the norm than bad, and campaigns wouldn't nearly be as enjoyable if there was nothing more to learn, explore or experience.

Just, make sure your player know afterwards if you changed a monster, so he doesn't start assuming things. If your hags are nice, make sure the player knows hags are usually evil, just so he won't make the wrong assumption in another game...

... Scratch that, I'd love to have a player SUPER excited about meeting and conversing with a hag. xD

[Tawmis]

Yeah, you got me :S
After some amount of self-reflection, I realized my opinion comes from one bad session involving a "custom dragon" many years ago. I guess I'm just still bitter that for some of the other players that thing we fought was their first exposure to fighting a dragon as the hero of a story. I would've been OK with it if the novice DM at the time had some creative reasons for the changes he made, or a rich backstory or relevance to the plot. But no. It was awful, and it was terrible to see the creature that I usually spend MONTHS creating an aura of terror and mystery around to be introduced and dealt with within an hour. So, guess you can call it an illogical pet peeve?
I now know that it's unresonable and illogical, and I'll try to remember that in the future. More good things come out of creatively changing the norm than bad, and campaigns wouldn't nearly be as enjoyable if there was nothing more to learn, explore or experience.
Just, make sure your player know afterwards if you changed a monster, so he doesn't start assuming things. If your hags are nice, make sure the player knows hags are usually evil, just so he won't make the wrong assumption in another game...
... Scratch that, I'd love to have a player SUPER excited about meeting and conversing with a hag. xD

To be clear though - I also do understand where you were coming from. After all, if you as a DM throw a troll at them where it's silver weapons that hurt them (through some process of evolution, or maybe because these trolls live in a volcano area, it's natural that they developed an immunity or resistance to fire, but a weakness to something else) - if those players are new to D&D, they may go to another DM's session and be like, "What do you mean fire hurts them? In the campaign I played in, they were even resistant to fire because they lived in a volcano cave!" (But even Morden's Book o' Foes has several versions of trolls - such as Dire Trolls, Rot Troll, Venom Troll, and Spirit Troll)... But yes, I'd say telling them after the game, out of character, that these were custom trolls that took refuge in this cavern long ago, fleeing from some war, and over time, developed a resistance to fire, but the chemicals from the smoke and ash and other elements from the volcano, had over time, made them weak to silver weapons (sticking with my same example).

And it's funny you mention a hag - my group at work I DM'ed for, took down a (Green) Hag way too easily... so now I am working on an idea that the Coven she belonged to is going after the party to seek revenge...

[djreynolds]

The game is all about resources. Make resting tougher.

Leomund's Tiny Hut can be dispelled, by a high enough caster. It can be cheesy, but its an effective way so players cannot just power through everything.

I found in OotA that the presence of the drow hunting party helped to press the party along because they were incapable of defeating drow for some levels. So you can have a hounding adversary after them.

[KorvinStarmast]

How do you instill fear into gamers?

1. Flood the basement.
2. Leave some piles of dog poop around and stick polyhedral dice into them so that it looks like the dog at the dice bage.
3. Close the nearby pizza shop.
4. Ban sodas and chips from your house.

[Segev]

From the OP, it's less that you wish to instill fear (which is a matter of atmosphere) and more that you wish to instill a sense of caution and threat assessment. Fortunately, 5e provides you with some safety net to give them the information they need: as long as your monster can't do the target character's maximum hp in a single blow, you can have it smack their tank so hard that he KOs early. This amount of damage output will usually signal "you're not ready for this" to the players, and the goal becomes grabbing their ally and getting out of there while he recovers. If they find this thing again, they'll likely withdraw, unless and until they've leveled up a lot.

If you want them to decide to withdraw without so much as engaging, without knowing what the enemy is really capable of, you have to provide evidence of its danger level. This works best with creatures that have weird abilities, particularly save-or-suck types. Yellow Musk Zombies and nearby yellow flowers will usually get PCs edging away. Stone statues haphazardly scattered about, particularly if they look aggressive or afraid, makes them worry about basilisks, medusas, gorgons, or cockatrices. Things that are particularly big or which announce their presence with noise long before they're seen also can cause some players to choose caution over predatory instinct.