Are there currently any plans to implement creature initiative, like in H5? (Asking because I remember it being mentioned somewhere.) That would add a whole new dimension of gameplay for mods. I’d be interested in implementing it, and make a mod based on it.
Previous discussion on this topic:
[forum.vcmi.eu/t/new-creature-stat-initiative/562/1)
Perhaps implement it as subtype of speed bonus?
{ “type” : “SPEED”, “val” : 1, “subtype” : 0} - increases both initiative and speed. So H3 and all mods unaware of initiative will still work as intended (because subtype value defaults to 0)
{ “type” : “SPEED”, “val” : 1, “subtype” : 1} - increases speed only
{ “type” : “SPEED”, “val” : 1, “subtype” : 2} - increases initiative only
We have something like this for damage where subtype = 0 increases both min and max damage while subtype 1 and 2 increases min/max separately. So something similar for speed should be possible.
But I would suggest to wait for reply from somebody who knows bonus system better than me (Tow or Warmonger).
That sounds like a reasonable way of implementing it. If there is no mod present, which specifies any other subtype for SPEED other than 0, everything would work as in original H3. I can’t think of any situation where that wouldn’t be the case.
But I’m not sure if everyone who posted in the thread you linked to has the same idea of initiative as I. My intention is to have it like in H5, where different creatures get turns at different frequencies. It seemed like some intended it to only determine the order of creatures’ turns.
I’m not sure if H5-style initative can be achieved easily - to implement it you need to completely remove concept of rounds in battle. This may not be as easy as it seems.
For example this will drastically change game mechanics and most likely will break existing balance of battles by making all high-speed creatures extremely powerful. There are also a lot of points to consider - like what to do with spellcasting?
Because of this making speed and initiative separate parameters while keeping battle rounds is a better idea - chance to run into some unexpected situations is much lower. Consider this to be H6-style initiative 
I think both types of initiative could exist; one of them should be renamed to something else, though. For this post I’ll call them H5 and H6 initiative respectively.
By default, all creatures would have the same H5 initiative. If the H5 initiative can’t determine which creature would get its turn first (which would be the case ), the H6 initiative applies. H6 initiative would work as posted above, with all speed bonuses usually increasing both actual speed and H6 initiative, unless otherwise specified.
Rounds could still exist even with H5 initiative, the only issue would be the absence of a 1:1 correspondence between rounds and creature turns. For example spell duration could still work as it currently does. Imagine an invisible creature, with the default H5 initiative, and the minimum H6 initiative. When that creature would get its turn, a new round begins.
What about spellcasting? If hero casted spell just before end of round when he should be able to cast it again? 1 round later or as soon as round ends? Should hero have his own turn or not?
H3 has some special rules for siege machines & towers that don’t use speed (or initiative) to determine turn order. Instead rounds are split into phases: catapult, tower, all units, rest of war machines.
What about “waiting”? Current form is pointless with initiative. In H5 waiting resulted in creature losing 0.5 initiative points (as opposed to losing 1.0 on normal action).
These are most obvious issues that I can remember right now.
What about trying to implement H6 initiative first before rushing into unknown and debatable? Because IMO implementing H5-like initiative without breaking H3 mechanics is impossible or close to it.
We were all talking about H6 initiative. It is way more popular and much, much simpler to implement without big changes to H3 code.
That being said, no-one said you cannot wish/have your H5 style one :). And to implement it if I remember it correctly, you just need another function that handles turn order. (One for H3/H6 and another for H5)? Could it work this way?
Where you see problems, I find solutions.
Honestly, VCMI team has done/is doing/will do an amazing job. You are intelligent enough to find solutions that you consider fair and implement them in a H5 or H6 sytem. I would not worry about it. When you think that you have done the most important things of VCMI, we all will encourage you to produce a H5/H6 battle system. It is not very easy and will consume time to get a good balance, but you have done the most difficult things.
The biggest problem I see are the artillery and spell casting. Mainly the hero (we can give initiative to war machines too, like in H5), because it is necessary to change the process, but it is possible to sort it out.
And H5 heroes can cast only when they have turn. In H5 battles aren’t based on turns like H3 or H6. H5 Initiative doesn’t allow tier 7 to cross all battlefied like in H3. Initiative define when creature is able to move and speed define how many hexes can move. For e.g H5 Archangel can reach max half of battlefied.
When I think about it, I realize that the two types of initiative are very different. H6 initiative could be present in the game by default without changing game mechanics, if implemented the way Ivan suggested. It is not what I had in mind when making this thread, but I suppose it would be nice for me to start out by implementing something simpler.
On the other hand, I think H5 initiative would be a very good module, as I read about on a wiki page (is that part still relevant?).
That is the beauty of H6 like initiative. A few changes (that could live easily with H3 speed), that produce a very nice outcome.