I love the structure and basic ideas of the class, first of all. I do have various concerns, however.
Battlefield Insight has too many "if, then" clauses required for it to do anything. I'd either
*make it so that you apply insight dice regardless of hit or miss, and/or make the dice only be spent if you hit (or the ally decides whether to use the dice after hitting)
or
*raise the die up to at least a d10
Remember that the rogue is dealing that damage, on top of a lot of other really strong abilities, simply by hitting at least once per turn. Your insight dice are...much less likely to get used, than the rogues sneak attack dice. One die step is a very small difference comparatively. At level 20, you're talking about a difference of ~10 damage, on average.
You also aren't as often actually adding that many dice to an individual round of damage dealing.
Alright, you and
@Garthanos have convince me to move up to D10.
As for Battlefield Insight itself, how about
"Once per turn when you inflict damage to a creature, you can apply your Insight Dice to it. If the creature already has Insight Dice applied to it, they are replaced by yours. You apply a number of Insight Dice as shown in the Insight Dice collumn of the Warlord Table. At first level that is 1d10. An ally who inflicts damage to a creature with Insight Dice on it may choose to exploit the Insight, If they do so, they can add as many of the Insight Dice they choose to their damage, expending the dice. Insight Dice on a creature disappear at the start of your turn, if the creature drops to 0 hit points, or if you are incapacitated."
The only thing missing would be the part where you can expend an Insight Dice to gain advantage, but in turn it would offer Caster support.
Shouts and Signals are interesting. Why not have a clause that you can put Insight Dice on a target if they are targeted by an attack granted to an ally by you? Or perhaps just say, you can use Battlefield Insight on a target you can see within X feet whenever you take the Attack Action. That way, regardless of what you do with your Attack Action, you can be applying the core ability of the class. Especially since Signals require Insight Dice to even use.
Right now, Shouts and Signals work directly against eachother until level 5. That is really the main thing that would make me reluctant to play this class, as it is. I don't want my core class features to be mutually exclusive.
I kinda wanted the 'free Insight on any action' to be the Chosen One's thing. Plus, then it messes up with the balance of 'two attacks needed to do more than Sneak Attack damage' so it's either free Insight or higher dice.
I wanted to allow Shouts and Signals to not compete by adding 0 dice signals, but it's possible there's just not enough of them?
Heck, I even considered ditching Signals in their entirety at one point and jut have more shouts but I kinda like having Bonus Actions and I wasn't just what to replace them with as far as features go.
If the int requirement of Signals there for balance, or flavor? Because IRL a dog could probably be taught these things and in dnd said dog would have an int of 3 or something. Maybe require an extra hour per signal for int below 6? Or an animal handling check or the help of a character who the animal trusts and takes commands from?
It was mostly for flavor reason, but the dog thing is a good point... I think the simpliest would be int of 3.
Some of the signals, like pin the legs, are going to be confusing for a lot of players. Is the idea for the class to be "advanced", with a steeper learning curve than other 5e classes? If not, maybe it should just cost 1 die, halve their speed or deny them the ability to disengage, and allow you to spend more insight dice later on to hinder them further or continue the effect. Also, a lot of these should require a save. Without that, they're more powerful than a lot of battlemaster maneuvers.
Well it IS indeed supposed to be more advanced... But what I could do is take Pin the Legs and split the effects and make them two different basic signals so you basically 'upgrade' to the one that does both and then maybe add a clause in Coded Signals that let you replace signals when you level up so you can trade those in.
They do seem more powerful than Battlemaster Maneuvers, but they do require YOU to hit with an attack to put Insight Dice (all the condition ones require dice expenditure), then that your allies inflicts damage AND, unlike Battlemaster Maneuvers, they LOWER your maximum damage instead of increasing it because you trade Insight Dice to use them. So I think the saving throw is just replaced by the second attack. 'Strike the nerves' and 'Addle' are essentially a version of a 'called shot' system, for exemple.
I'm not sure the balance works out of allowing someone to draw and use an object as a reaction having no cost beyond your bonus action.
Hmm... what if it instead grants the ally the ability to use an item as a bonus action then? I was trying to find some 0 dice signals that you wouldn't use all the time.
Why No Synergy With Casters? I know this was an item of contention in my own marshal thread, but it just makes no sense to me that such a character would not no idea, unless utterly specialised in doing so, how to get more out of the spellcasters around them. Strike! could easily allow an extra spell attack that deals 1 of the same die of the same damage type if the ally casts a cantrip that requires an attack roll, for instance.
Or, a shout that simply increases the chance to hit and the damage of the ally's next attack, and don't specify attack action or weapon attack.
I wanted a bit more synergy with casters (the signals that inflict disadvantage on saves count in my eyes), especially in the signals, but it's just really REALLY wordy to try to include Spellcasters because: sometimes they attack, sometimes they ask for a saving throw; sometimes they inflict damage, sometimes they don't; sometimes they affect enemies, sometimes they affect allies; sometimes they use cantrips, sometimes they spend spell slots. Basically there's plenty of wording you need to consider and could cover. It gets really difficult so I could really use some help on that front.
The rest looks good, but I'm not as worried about anything above level 5 or 6 in a class.
Any comment on the flavour of the subclasses?