What spells or other effects cause a creature to make a saving throw to avoid being knocked out?

I saw that a hydra has "advantage on saving throws against being… knocked unconscious" and was curious as to what spells or effects would cause such a thing to happen. The only effect that came to mind is the sleep spell, which operates on hit points rather than a saving throw. What else can knock a creature unconscious?

How can I design a magical weapon that grants an advantage against fire-base creatures without using water and choking effects?

The party I am DM’ing is going for an adventure to the Elemental Plane of Fire. I want to design a magical weapon that can grant an advantage against fire-based creatures. I see that Fire Elementals have Water Susceptibility (Cold Damage) but I have already house-ruled that elemental planes can not include magical effects of elements from other elemental planes, but just the spells that have elements of the current plane can be cast (as the plane purely consists of element of itself). For example, in the Elemental Plane of Air, not only Earth-based spells but all the spells are impeded, except air-based ones.

After I realized that I can’t use a magical weapon that has cold damage due to my house-rule, I wanted to give the weapon a "heavy smoke" effect to choke the fire, as I thought that fire can not live without oxygen. But this option conflicts with my house-rule, also I saw that the fire-based creatures any other fire source in the Elemental Plane of Fire don’t need air to live.

Now I have no idea how can I design a magical weapon that gives an advantage against fire-based creatures without cold damage and choking the fire via leaving without oxygen is not an option. I can not cancel my house-ruling because of the sake of my setting. I am open to any house ruling ideas beside the official ruling.

TLDR: as in title, how can I design a magical weapon that grants an advantage against fire-base creatures without using water and choking effects?

If the question shows up to be opinion-based, please accept my apologies.

Are there any attacks or effects that reduce max HP to 0 without stating what happens?

Inspired by PJRZ’s comment on this answer to this question:

What attacks actually exist that reduce someone’s max HP, but do not specifically state what happens at max HP of 0?

As far as I am aware, all monster abilities that can reduce max HP to 0 state that the creature dies (and optionally may be brought back as some undead creature, depending on the exact creature/attack used to reduce the max HP to 0).

As an example of an attack that does state what happens, consider a Wraith’s Life Drain attack (MM, pg. 302):

Life Drain. Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit: 21 (4d8 + 3) necrotic damage. The target must succeed on a DC 14 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

Are there any attacks or effect that reduce a creature’s max HP to 0, but do not address whether or not the target dies?

Do Summoned creatures trigger “on death” effects?

Taking Leshies as an example, they can be summoned with the Summon Plant or Fungus spell. They also have the Verdant Burst ability (abbreviated):

When a leaf leshy dies, a burst of primal energy explodes from its body

The entry is slightly different for each form of Leshy, but they all give an instantaneous healing effect to nearby plant creatures, and most cause the area to become difficult terrain for 24 hours or permanently.

However, they also gain the Summoned trait, which states:

They are automatically banished if reduced to 0 Hit Points or if the spell that called them ends.

Which of these triggers first? What if the leshy is killed by massive damage? Is there a distinction between the instantaneous healing and the lingering difficult terrain (if the healing occurs, is the terrain then banished with the Leshy)?

Does the pressurized lung augmentation in Starfinder protect a character from the effects of sudden decompression?

According to the Starfinder rules, the pressurized lungs biotech augmentation has the following effect:

"You can hold your breath for up to 1 hour and are immune to the normal environmental effects of being in a vacuum."

The rules on vacuums are as follows:

Vacuum

The void of space is effectively empty of matter, and this vacuum is perhaps the greatest danger of outer space. A creature introduced to a vacuum immediately begins to suffocate (see Suffocation and Drowning) and takes 1d6 bludgeoning damage per round (no saving throw). Because a vacuum has no effective temperature, the void of outer space presents no dangers from cold temperatures. A creature retains its body heat for several hours in a vacuum. Sound doesn’t travel in a vacuum.

Decompression occurs when a creature suddenly transitions from a pressurized environment to a vacuum, such as by being flung out of an airlock or being inside a sealed structure that becomes heavily damaged. Such a creature takes 3d6 bludgeoning damage (no saving throw) in addition to any suffocation damage.

Most creatures travel the vacuum of space in a starship.

Do the 3d6 points suffered from sudden decompression (discussed in the second paragraph under Vacuum) count as the "normal environmental effects of being in a vacuum"? Or do normal environmental effects only pertain to the suffoction and 1d6 per round?


Here is an article about the real science.

It is logical for lungs that hold an hour’s worth of air to protect you from suffocation in a vacuum, and they theoretically could stop your lungs from bursting (another danger in a vacuum). I don’t see how they would prevent your blood from vaporizing and stopping circulation. Scientifically, even with pressurized lungs, the vacuum should damage/kill you. Granted, it is a fantasy game.

What’s the extent of things that a charmed creature would do for you under the effects of the *awakened* spell?

Unlike other charms, with awaken you can literally transform a beast or plant into higher-intelligence form of life. For example, an awakened tree gets to have intelligence like humans, limbs, ways to communicate and so on. It gives them freedom they never had.

Do they see the caster as their creator or something? If the caster asks the awakened tree to help in combat, or fight monsters as an ally, would they do it?

How exactly do cylinder spells and effects “ignore obstructions” in their areas? Or what kinds of obstructions they can realistically ignore?

So, Spell descriptions on Area entry says:

When casting a cylinder-shaped spell, you select the spell’s point of origin. This point is the center of a horizontal circle, and the spell shoots down from the circle, filling a cylinder. A cylinder-shaped spell ignores any obstructions within its area.

I feel like "any" is a bit to strong claim for how it does actually work.

Could someone elaborate step-by-step, how do you actually target such a spell when there are:

  • a low wall in a spell’s area;
  • a wall, higher than the height of cylinder’s point of origin, selected by a caster;
  • ceiling above one of desireable "targets", but lower then a mentioned point of origin?

Should all of them really be ignored?

Is the target of Sanctuary aware of the spell effects?

I am playing a Cleric and regularly use the spell Sanctuary on low life teammates while telling them to back away to safety (short call so I can heal them up and they will stop attacking and avoid breaking the effect).

I had one time when I had to choose whether to say to my Sanctuary target to run away or alert another character from a danger that only my character perceived. I choosed to alert my target but it lead our Wizard to be critically stabbed (he’s fine, merely a flesh wound)

So I was wondering, is the target of Sanctuary aware of the spell effect or should I continue telling them not to break the effect ? If they are aware of the effect, do they just "feel protected" ? Do they also get the intuition that being harmful to another creature will break this protection ?