Many ways around LTH (Leomund's Tiny Hut).
Objects: DMG 246
For the Purpose of these rules, an object is a discrete, inanimate
item like a window, door, sword, book, table, chair, or stone, not a
building or a vehicle that is composed of many other objects.
Thus ordinary air does not count as an "object". It is not discrete nor inanimate. Same for the water in a pond, the flames gushing out of primitive flamethrower, or the output of breath weapons: those also do not count as "objects".
Since LTH lists that it blocks objects, then any of those things will work against a party protected by LTH. Let's say, a glass bottle containing a liquid that, on contact with air, quickly turns into a large amount of poisonous gas. Throwed against the dome and it would work nicely: the bottle breaks at the outside surface, and the resulting poisonous gas would just seep inside. Lots of delivery ways to throw the glass container from further away: catapult-like devices, custom made arrowheads, etc.
Another anti-LTH tactic for humanoïd baddies: set a large amount of foliage and semi-wet wood, or even the whole forest, aflame, in order to smoke the PCs out! Any type of fine dust cloud, fine enough that you don't count each grain of dust as "an object" but rather the entire cloud as a gas, something that makes it hard to breathe, will work, too.
PHB 255 on LTH spell:
The atmosphere inside the space is comfortable and dry, regardless of the weather outside.
Comfortable here is related to the outside weather. Temperature, wind, humidity, that sort of thing. The rule doesn't automatically imply that the atmoshere also gets "filtered" out of any artificial toxicity or poisons, unless the DM decides so.
If you think LTH makes non-humanoïd night encounters trivial, then make the game world have low-level and higher-level areas. Low levels adventure, a mundane forest fillled with mundane animals. Higher level the PCs might have to cross the very dangerous Northern Forest, where there are much less mundane animals and much more fantastic and much more cunning animals. Your pack of ordinary wolves, active at night, are suddenly replaced with Winter Wolves, which have a cold breath weapon.
All that being said, players hate it when the DM likes to use night time encounters to interrupt and ruin their rest. It often feels forced just to pile up extra trouble upon them at their weakest moment.
Logicallly the amount of encounters is based not only on the mere density of monsters in the area, but also on covered ground, and how detectable a group is.
We can see 3 types of encounters:
- Moving party and moving monsters find each other, maybe one side surprises the other.
- Moving party finds immobile monsters.
- Moving monsters find immobile party (during breaks, longer conversations, etc.).
- Moving monsters find immobile party.
Another factor is that when the party is moving, it is more visible and noisy than when they are bunkered up for the night.
All this naturally means that there should be a LOT less "random" night encounters than "random" day encounters. A good DM should thus use night encounters either quite sparingly, or with solid hints to the players, like say an NPC telling them that the forest they are going into is full of nocturnal goblins.
In my campaigns (typically lower epic magic than vanilla D&D), LTH caused so much headaches, I just ended up changing it like this:
Material component: Added a 2-person Tent (2 gp, 20 lb).
Area: 3x3 squares of empty relatively flat open unencumbered terrain.
At 1st round of effect: Tent transforms into a wooden hut. This takes the entire round.
The hut's front side has a 2' wide 6' tall wooden door. The back side has a 2'x2' window located around 5' height (or at caster's level). Both door and window open outwards. The door can be "locked" by a very simple rotating lever on the inside side frame that rotates down into a simple slightly jutting L shaped part in the door. Same for the window. Pick Locks DC 10 to open it.
Interior is 3x3 squares, with a slightly sloping roof. Hut has a wooden floor, directly on the ground.
The atmosphere inside the hut comfortable and dry, regardless of the weather outside.
The hut counts as a single Large object with AC 15 and 27 Hit Points. If destroyed, the entire hut falls down, breaking apart without dealing any damage to those inside. One round later, nothing remains of the hut. Any part that is separated from the rest of the hut, also breaks down in the same manner.
If not destroyed, at the last round of the effect the hut, over one complete round, transforms back into the original tent. No damage on the hut gets carrried back over to the tent.
Basically, the spell turns back into its original purpose: easy camping site with protection against the weather, and a bit of protection against enemies, and not a impregnable fortress.