Yes, Snakes can be prone
Prone is a condition (PHB, 290). And the only way to avoid that condition is to have some form of immunity or something else mechanically that prevents a creature from getting the condition.
For creatures, the statblock lists Condition immunities (if there are any). Spells, items, etc. will also state if there are any ...
There are no specific rules for what happens if knocked prone while swimming, therefore, from a purely mechanical standpoint, we must assume that the general rule applies.
From PHB 292...
A prone creature's only movement option is to crawl, unless it stands up and thereby ends the condition. (Note: Crawling costs 2 feet of movement per foot moved. ...
A Prone Creature can Dodge
Nothing in the rules specifies that a creature cannot take the Dodge action while under the effects of the Prone condition.
The Prone condition (PHB, p. 292) states:
A prone creature's only movement is to crawl, unless it stands up and thereby ends the condition.
The creature has disadvantage on attack rolls.
An attack ...
There are two different things happening here: your movement speed being halved, and spending half your movement speed. These work differently, and the order matters. The end result is that the grappler can't move-drag after standing up from prone. Here's how it works:
You start with your full movement speed.
Let's use 60′ for the sake of example.
The rules that you've quoted are pretty clear. You gain advantage when attacking unconscious creatures, and you gain disadvantage when attacking prone creatures from further than 5 feet away. If you have both advantage and disadvantage — you're attacking an unconscious creature from further than 5 feet away — you get neither, instead.
Yes you can
PHB Chapter 9: Combat, page 193, emphasis mine:
Your character can do things not covered by the actions in
this chapter, such as breaking down doors, intimidating
enemies, sensing weaknesses in magical defenses, or calling
for a parley with a foe. The only limits to the actions you can
attempt are your imagination and your character's ...
Arguably, the rogue may stand up
The character is not literally "granted a resource" that is called movement but that is in fact the way the rules of movement talk about how it is used:
However you're moving, you deduct the distance of each part of your move from your speed until it is used up or until you are done moving.
In practice, movement is a ...
No, a surprised character can't drop prone
As you posted, Surprise says:
If you're surprised, you can't move or take an action...
This "can't move" terminology is actually used a lot in the rules. A few other examples:
The creature is incapacitated (see the condition), can't move or speak, and is unaware of its surroundings.
Yes, it's halved
Mobile: [...] Your speed increases by 10 feet.
Prone: [..] Standing up [from prone] takes more effort; doing so costs an amount of movement equal to half your speed. For example, if your speed is 30 feet, you must spend 15 feet of movement to stand up.
So mobile increases your speed, and prone costs you half your speed. If you ...
The same thing as any other prone creature
Jeremy Crawford has confirmed the answer that follows as a correct interpretation:
If you're knocked prone underwater, you're subjected to the effects of the prone condition as normal. One way to visualize it is that you're floundering.
There are no conditions/rules/restriction in the game ...
Yes, you can absolutely Dash while prone. If you don't want to spend half your speed to stand up, you can still crawl (from PHB, 191)
To move while prone, you must crawl or use magic such as teleportation. Every foot of movement while crawling costs 1 extra foot.
To stand up, you use half your speed (PHB, 190)
Standing up takes more ...
As mentioned in other answers, the Monster Manual generally states when a creature is immune to a certain condition, such as prone.
Therefore, since this is not the case for the snake, it isn't considered to be immune to the prone condition.
Also, to address the first part of your question - no, a snake is not considered prone all the time, otherwise this ...
Yes, you can attack while prone. As it describes in the PHB's definition of the prone condition on page 292:
The creature has disadvantage on attack rolls.
So you may attack while prone, but with disadvantage.
If I were to cast levitate on a prone orc and float him 20 feet into the air - would he still be prone? - Yes
Jeremy Crawford has clarified:
You can almost always be knocked prone. About the only time it's physically impossible for you to be knocked prone is when you're affixed to something that keeps you upright.
Being underwater doesn'...
Incapacitated will prevent opportunity attacks
Your player is correct. The opportunity attack requires a Reaction. And Tasha's Hideous Laughter's description states (PHB, p. 280, bold added):
The target must succeed on a Wisdom saving throw or fall prone, becoming incapacitated and unable to stand up for the duration.
And the "incapacitated" status ...
Neither the description of shoving enemies nor of the prone condition have any mention that a prone enemy can't be shoved. So going by the letter of the rules, it is indeed possible to shove a prone creature.
(Though given circumstances of what is supposed to happen in the action of the adventure, GMs are entirely in their right to overrule such an outcome ...
As you mentioned, to stand up:
[you spend] an amount of movement equal to half your speed.
The rules for prone movement (including standing up) are listed under Movement and Position in the Player's Handbook, right between moving through Difficult Terrain and Moving Around Other Creatures. In my interpretation, I see no reason to disqualify ...
Yes, if the creature is trained in Acrobatics.
It's because of this Acrobatics ability:
REDUCE FALLING DAMAGE (Trained only)
If a creature that has training in Acrobatics falls, it can make an Acrobatics check to reduce the amount of falling damage it takes. The creature can make this check whether or not the fall is intentional.
Yes, a prone immobilized creature can stand up.
The definition for Immobilized could seem a little fuzzy upon first reading:
When a creature is immobilized, it can’t move, unless it teleports or is pulled, pushed, or slid.
Until you note that Move is explicitly defined:
Any instance of movement, whether it is done willingly or unwillingly. Whenever a ...
Once a creature stands up they no longer suffer any effects from being knocked prone
Your reading is correct. A creature can get up from prone on their turn by spending half their movement, and once they're standing up again they don't suffer any further consequences from having been knocked prone. As you've observed, with an unhelpful initiative order, an ...
The rules simply didn't take the flying case into account. You'll notice there is no reference in any of the entries in the table to losing a wing instead of an arm. I think it was simply written before these flying races became playable.
The highlighted text makes perfect sense if you are restricted to using your legs to move around but makes no sense if ...
From the Player's Basic Rules (v0.2), page 71:
If a flying creature is knocked prone, has its speed reduced to 0, or is otherwise deprived of the ability to move, the creature falls, unless it has the ability to hover or it is being held aloft by magic, such as the fly spell.
So a flying creature that is knocked prone will fall, unless it has the ability ...
I don't see any specific rules definitions for "movement." Based on definitions in other editions, my opinion is that a character "moves" when they walk or use some other "special type of movement" such as jumping, flight, swimming, etc: when they move from their original position, rather than just standing up, dismounting, or otherwise reconfiguring ...
Rules As Intended (RAI) - Standing up costs movement equal to 1/2 your highest speed
Jeremy Crawford has put out an official clarification which says:
The rule on standing up from prone fails to account for you having multiple speeds. Here's the intent: if you have multiple speeds and stand up, expend an amount of movement equal to half your highest ...
You can Dodge when Prone
The rules for the Dodge action simply state:
When you take the Dodge action, you focus entirely on avoiding attacks. Until the start of your next turn, any attack roll made against you has disadvantage if you can see the attacker, and you make Dexterity saving throws with advantage. You lose this benefit if you are incapacitated ...
Get creative with improvising during combat.
Fifth edition codifies a list of actions you can take in combat, but these are explicitly non-exhaustive:
The only limits to the actions you can attempt are your imagination and your character's ability scores. [...] When you describe an action not detailed elsewhere in the rules, the DM tells you whether that ...
According to the implications of the Jeremy Crawford ruling below, standing up from prone does not trigger booming blade. This is because the trigger requires the target creature to move, but even though standing up costs the target movement it does not actually move the target anywhere.
Question: For Booming Blade, did you intend for standing up from ...
Charge as a regular action
You found what there is to find: "Charge" is not a regular action you can take.
The common conception seems to be that a player character is not big enough to charge something efficiently. In fact, most (to not say all - I couldn't find any that wasn't at least Large, but I don't like saying "all") of the beasts with the Charge ...
No, you cannot move via Lightning Rush while prone. You can use Lightning Rush against the enemy adjacent to you as the Move part is an effect. Being unable to do it does not limit your attack in any way.
Effect: Before the attack, you move your speed to a square adjacent to the triggering enemy.
Ok, so before the attack you move, what ...
Safety trumps immersion
Falling down is not risk free: limbs can beak, backs or heads can get injured, and arterial spry can fountain. The latter did happen in a LRP due to a fall due to collision with a well hidden BBQ frame. You want to make sure your friend is safe. As an organiser, you definitely want the people who pay you for the privilege of playing ...