Our GM has us roll new initiative every round. Just how broad of a change is this?

Question

I am playing in a campaign based on Pathfinder 2nd edition rules. My GM decided to introduce the house rule of rolling initiative every round, basically altering one of the base concept of the game.

The result so far is that every round is very different from the others and in my opinion the dynamic range of possible outcomes greatly increases.

But just how broad of a change is this? What else can we expect this house rule to change about the game?

For reference:

• The same skill is used to roll initiative each round.
• End of turn effects will still end after the relevant creature's turn.
• Unconscious creatures will roll to stabilize etc. at the end of a round.

Answer 1

This is a Massive Change

While it might seem like a small change, this is actually a massive change. There are numerous effects that end at the start of a turn or end of a turn that can be massively affected by initiative order, and some abilities will be outright overpowered unless also house ruled. While an exhaustive list of effects would be probably hundreds of pages, I'll just list a few significant ones here:

Initiative Feats and Abilities

Some feats and abilities trigger "when you roll initiative". A safe bet to house rule all of these is to limit them to the first round of combat, but unless otherwise modified, there are some potentially overly powerful feats. These include Swaggering Initiative (free weapon draw once/round instead of once/fight), After You (panache EVERY ROUND for simply going last), and the Triumph Siktempora's Uncanny Pounce (two free actions every round). Really, there are many of these abilities, but basically all of them should be sane if limited to just the first round.

Effect Timing

Certain effects last until the "start/end of your next turn", or the same but for the target's turn. These can be drastically reduced in effectiveness depending on your relative initiative positions. Take the ever common Raise A Shield action. If you are last in a round, and spend an action to raise a shield, then roll the highest in the next round... you just wasted your action. Conversely, if you are first in a round, raise your shield, then last in the next, you just got two rounds worth of value for that one raise a shield action. This applies to other actions, like Inspire Courage, or Guidance, even making things like Aid potentially unreliable if your ally doesn't get a turn before your next turn. There's not going to be a consistent rule to re-balance all of these - instead, creatures with abilities like these will only be incentivized to use them if they roll high initiative, and dis-incentivized if they roll low. This will lead to more meta-strategy: strategic decisions your character makes because of the rules of the game instead of in-world situations.

Frightened and Persistent Damage

Let's say I am second to last. After me is the monster, so naturally I Demoralize it. I critically succeed! The monster then goes, reducing it's frightened value to 1 at the end of its turn. Then rolls top initiative, reducing it to 0 at the end of its turn... my allies had no opportunity to capitalize on that! Conversely, if I have a Wounding rune (or other means of reliably applying persistent damage), then if I benefit less from going twice in a row than others would, since persistent damage doesn't stack. However, I get more benefit from the monster going twice before me than another would, since it's more likely I'll be able to re-apply my persistent damage. There's no house rule I can think of to fix these interactions - these again will increase the amount of meta-strategy, and increase the amount of unpredictability in general.

Stealth - Constantly Sneaking?

If you roll Stealth for initiative past the first round, do you get to become hidden if you beat Perception DCs? If not, why are you rolling Stealth anyway? This rule would need changed in some way.

Dying

If a monster takes out a PC, and that monster is last in initiative, with your current rule the PC would have to immediately make a stabilization check. This can result in a lot of deaths that would otherwise be react-able by the players. For example, if you go down to a crit (a common occurrence), then critically fail your recovery check, or are any level of doomed... you're toast. The remedy for this is less clear - I'd suggest that the players makes their recovery check starting at the end of the next round. This guarantees everything a chance to react to the dying player, sometimes multiple times, and makes the dying player more likely to miss turns. But it's easyish to remember and better than dying!

Swingy-ness, aka How The Party TPK'd

The biggest potential, non-mitigatable downside is that this makes the game more swingy as a whole. It's entirely possible for you to not get a turn between two of the big bad's turns. It's even possible for no one in your party to have a turn between two of the big bad's turns. Given how big bad's tend to be stronger than any individual PC (averaging at least 1 level above the party in my experience, to sometimes as high as 4), two turns can wreck a party. A dragon that breathe weapons, makes a no-map attack (three actions), then on the next turn does a draconic frenzy can easily take multiple party members down to 0 HP. Randomness like this will only hurt the players in the long run - it's more opportunities for things to go wrong in a way that they can't react to. That's my biggest worry about this house rule - enemies having back-to-back turns prevents the players from being able to react, and there's nothing less exciting than watching your characters die without being able to do anything at all about it.

Is This a Bad Rule?

Given the amount of things discussed above (which is just a subset), you might be tempted to think this is a unworkable house rule. However, if you accept meta-strategy as a fun and acceptable piece of the game and avoid uber-bosses (i.e. level+3 or higher enemies), it should mostly work out okay! It creates more randomness - some players will enjoy that, some will hate it. It's up to the GM to know their players.

Suggested Accompanying House-rules

If I were to run a game with the house-rules you described, I would add some more house-rules to maintain balance. I would add the following rules:

1. Any feat that has you take additional actions based on "rolling initiative" only provides those actions in the first round. Alternatively, all feats that modify initiative only work the first round.
2. Only Perception for initiative after the first round. This makes Perception vastly more important than it already is, but it makes the most narrative sense, and requires the fewest rule changes to make Stealth initiatives work.
3. Recovery checks start at the end of the round after the round in which the player went down.

Answer 2

It used to be normal

Rolling initiative every round, to my knowledge, is uncommon in d20 versions of D&D, like dnd-3e, dnd-3.5e, and pathfinder. My experience of it is from AD&D 2e. I'd recommend that you look to what was done in those editions that natively used per-round initiative for inspiration.

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What's gone before

In previous editions of Dungeons and Dragons, like adnd-1e and adnd-2e, initiative was rolled every round (Advanced Dungeons & Dragons 2nd Edition Player's Handbook, 93), which were each supposed to be roughly a minute long (119). The variability seemed to be intentional, apparently to simulate the unpredictability and chaos that occurs during battle.

The default system was actually to have each side in a battle roll initiative, then the winning side would take their turn first. Modifiers existed to improve or degrade initiative for each side, and if the initiative came out the same, all actions happened simultaneously (94).

Two optional, more complicated, initiative procedures were available as well: Group Initiative; one roll, but with individual modifiers like weapon speed (94), and Individual Initiative; individually modified rolls for each creature.

I'd recommend this old rule to limit the 'swing':

If a creature had multiple attacks from multiple weapons, those attacks happened at once on its initiative. For a creature with multiple attacks from high levels, only its first attack happened on its initiative count; all creatures with multiple attacks acted again after the first set of actions in a round, in the same initiative order.

This old rule is hard to make fit

Spells had a casting time, usually a number which modified the initiative of the caster. Spells requiring one round to cast instead took effect at the end of the current round after all other actions. Some spells took 10 minutes (10 rounds) to cast, and taking damage, or failing a saving throw would (not could, would) interrupt the spell (85).

The d20 ruleset really doesn't look like it would fit that old rule very well. It's one of the things that when changed with the 3rd edition, intentionally or not, factored in to increase casters' power.

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In Summary

The effect of rolling initiative every round was largely unpredictability; especially for spellcasters, though it tended to balance out. Consider embracing the unpredictability as increasing the simulation of verisimilitude. As another answer mentions, holding initiative is an option that might improve predictability.

Take care not to go too slow though; going first sometimes means that your opposition can no longer take any actions.

Answer 3

One reason for using fixed initiative is simplicity.

The other thing to think about is that, under your new system, some creatures can get two turns back-to-back. If a dangerous monster attacks a character late in one initiative round, it could then attack the same character early in the next initiative round, doing a lot of damage before the character can react.

(I've played a lot of combat in game systems which use dynamic initiative, such as Gloomhaven, and I know that this is an important thing to consider.)

Interestingly, PF2e allows the delay action, where a character can simply decide to act later in the round. Normally this is bad because it permanently decreases your initiative count, but that doesn't appear to be a consideration if you have dynamic initiative. If you feel that you don't like the unpredictability of monsters potentially acting twice in between your actions, you can avoid it by simply delaying your initiative until you always go last in each round. (Unless your GM has house ruled this as well.)

I predict that your group will also sometimes see a tactical advantage from delaying -- for example if a monster is far away from you, your group will see benefit in delaying to force the monster to spend actions to move toward them, rather than vice versa.

In PF2e specifically, there are "two round spells" such as Summon Draconic Legion which are balanced assuming that enemies will get a turn to move away from them to avoid damage. With dynamic initiative, a caster can manipulate their initiative to make it less likely that the enemy will get a turn. You might attempt to patch this by saying that these two-round spells last exactly one round even if the caster's initiative changes. But you might feel that this is too much bookkeeping, and simply accept that the spells are stronger now.

You've asked:

what else do you think we should absolutely change to keep the game balanced?

There's nothing that you need to change -- the game seems reasonable as is. But you should probably check with your DM if the "delay" action is allowed, and if it is allowed then you should think about ways to use it tactically in combat.