What are the game playing impacts of allowing players to take turns out of initiative order? [duplicate]

As per a previous question I asked RAW do not allow players to go later in initiative order in 5E as they could in earlier editions of DnD and other roleplaying systems.

What are the potential things to consider if I choose to home brew changes to this behavior as part of my own rules?

The rule I am considering is as follows.

In a players turn they may either hold an action based on a trigger as per RAW or they can choose to delay there entire turn until after another stated players turn. A player may only delay once per round and cannot name a player Or NPC higher in initiative order to wait for. E G a 5 character combat 4 players and NPC roll initiative and are in order players 1 to 4(high to low) with the NPC sitting after player 3

Player 1 can choose to delay their turn and take it after players 2-4, or the NPC, they state they will go after player 3

On player 3 go they may choose to either go after player 4 or now, they cannot decide to go directly after player 1

Player 1 now takes their turn and must have a turn they may not choose to delay again.

Next round the players return to original initiative order.

In order to stick to stack guidelines I am looking for specific examples from players and GMs who have tried this rather then opinions.

How do I handle initiative when a new force joins a combat that’s already in progress?

I am DMing a small hunger-games-like adventure where there are multiple parties of NPC who also are participating. It is pretty likely that the PCs will happen upon some of the NPCs fighting some monsters.

How do I handle the PCs joining the fight, do I roll initiative all over again? Do I just roll for the new combatants and add them to the round?


Also see this similar question for Pathfinder:
How to handle some new NPCs who enter a fight in progress?

Does the Gloom Stalker ranger’s Dread Ambusher feature apply only when the party actually engages in combat, or when initiative is rolled?

The Gloom Stalker ranger’s Dread Ambusher feature says, in part (XGtE, p. 42; emphasis mine):

At the start of your first turn of each combat, your walking speed increases by 10 feet, which lasts until the end of that turn. If you take the Attack action on that turn, you can make one additional weapon attack as part of that action. If that attack hits, the target takes an extra 1d8 damage of the weapon’s damage type

If the DM calls for initiative to be rolled earlier than the party could reasonably engage in "combat" (such as a combat happening at the gates of a city far away, or off in the distance), can the ranger still benefit from Dread Ambusher once actual combat starts for the party/ranger?

The class feature itself doesn’t specify that the ranger needs cover, or surprise, and it doesn’t specifically say that the class feature starts on "initiative" but rather on the first turn of combat.

Or is the benefit of Dread Ambusher just gone if the DM decides to call for initiative more than a round before the ranger can engage in combat?

What is the mechanical reason for rolling the same initiative for a group of creatures?

The 5th ed Players handbook states that

The GM makes one roll for an entire group of identical creatures, so each member of the group acts at the same time.

Historically in other systems I have rolled initiative for all NPC’s individually, allowing for the fact some may react quicker then there counterparts.

Has the reason for this bulk rolling of NPCs ever been explained, or is it simply a mechanic to make things run smoother?

If an NPC and a PC roll identical initiative who goes first?

Normally, when 2 players roll identical initiative in combat, they decide between themselves the order they do things in and then stick to that on subsequent rounds.

How should the DM handle it if the NPC rolls the same initiative, especially if they are in combat directly with the player who rolled the identical initiative?

If rolling bulk initiative for a group of NPCs, how should identical rolls with players be handled here? It feels like a lot can swing on whether the GM chooses for the group of NPCs to attack the player before he can decide his action.

Can I use Flash of Genius on an initiative roll?

The Artificer’s Flash of Genius says:

When you or another creature you can see within 30 feet of you makes an ability check or a saving throw, you can use your reaction to add your Intelligence modifier to the roll.

On the one hand, an initiative roll is an ability check, which means that it’s eligible for Flash of Genius. However, it’s not clear whether I would have my reaction available as initiative is being rolled. So, can I use Flash of Genius to add to an initiative roll? Does it make a difference if I’m surprised?

Order of resolution of several identical initiative Attacks

It sometimes happens that several identical monsters, all using the same initiative, attack a single character.

In my games, this is often a volley of missile fire at a caster.

For pure practicality, I typically roll all the attack rolls together, count up the hits, and then roll all the damage, and assign it to the player as a single total. If the potential damage total is less than their current hit points, there is little difference between this approach and RAW.

However, when there is a potential for damage to render a character unconscious, this approach does differ substantially from RAW, at least for my understanding of them. RAW, I should roll each attack and record each instance of damage separately. Upon the first hit that renders the character unconscious, they immediately drop prone. The subsequent attacks, although occurring on the same initiative, in some sense come ‘after’ the character has fallen prone. Thus they are at disadvantage to hit (assuming missile attacks) but each one that does hit indicates a failed death save, so that three such hits would result in the character’s death.

Questions:

  1. Is my understanding of the situation with RAW correct?

  2. Is there any difference in this situation between multiple attackers on the same initiative and an attacker with multiattack?

  3. Suppose I choose to roll all attacks and damage at once, even in situations where the potential damage was more than a PC’s current hp. [In this case, the chance of the attackers hitting would increase, the chance of the PC going unconscious would increase, but the chance of the PC dying from failed death saves would decrease.] Can this decision be reconciled with (Initiative; PHB, p. 189):

    If a tie occurs, the DM decides the order among tied DM-controlled creatures,

    that is, I have decided to resolve these ties simultaneously? Or would such a choice violate RAW and require me to invoke Rule 0?

Related: How do creatures moving on the same initiative handle the effects of Sleep and Hypnotic Pattern?