Also note that this is very specifically mission timers. 'Soft' timers like Protect the Device being attacked by enemies aren't affected by the Chosen stopping the clock. (Naturally, this includes that they don't stop the Avenger's HP from ticking down during a Chosen-caused Avenger Defense mission) There's not many mission types with this kind of concern, and still fewer when you consider that Chosen can't jump eg classic Avenger Defense missions, but still, it's something to be aware of.
This is a mechanic that could've used some refinement, basically, but is mostly functional enough.
Anyway, moving on to...
Common Chosen Abilities
Before I start on abilities properly, I should note that the Chosen, though they have humanoid body plans and narratively all started out as humans, are actually immune to all effects that only work on humanoid enemies. (eg Justice on Skirmishers, Void Conduit on Templar) This is a relatively minor thing, but it can be an unpleasant surprise if eg you made decisions expecting to be able to Justice the Assassin out of Cover and into easy shooting range and whoops that plan you already partially committed to doesn't actually work!
Summon Reinforcements
The Chosen summons 1, 2, or 3 ADVENT Troopers, based on the Chosen's tier, with the Trooper tier affected by standard Force Level mechanics. These Troopers spawn adjacent to the Chosen, and immediately activate and scramble for Cover, even if they aren't visible to your soldiers. This is a completely free action that can be performed anytime the Chosen has at least one action point remaining, but has a cooldown of 3 turns. Replaced completely when a Chosen acquires a summoning Strength.
Oddly, while the Chosen actually have icons, names, and descriptions for most of their abilities, this isn't one of them. I'm borrowing a related Strength's icon, and have made up an appropriate name.
The exact mechanics of this capability are a bit strange and unintuitive, and further obscured by RNG being a non-trivial component: on any turn in which Chosen are capable of summoning reinforcements, it's entirely possible for them to, completely at random, just... not. Usually they'll summon reinforcements at the very first opportunity they get, but not always, and past that first summon they're particularly prone to refusing to summon more reinforcements even though their cooldown is done. (If the fight drags on that long, of course)
Part of what hides its mechanics is that Chosen are allowed to initiate the summons at any point in their turn so long as they have at least one action point, have already been 'activated', and in the Assassin's case aren't hidden by Vanishing Wind. That is, they can summon at the start of their turn, or move and then summon, or use a special ability that doesn't end the turn and then summon. I actually spent a while under the impression the Chosen operated on Sectopod mechanics of having 3 action points and almost nothing ending their turn (In part because of Freeze immediately breaking on them and claiming to have taken an action point, just like with a Sectopod), but no, they have two action points, and most of their actions end their turn. Summoning reinforcements is just free, is all.
Further obscuring the details from a learning player is the Assassin's Bending Reed, where she gets a Momentum-esque movement-only action point anytime she attacks in melee: this action point is enough to let her summon reinforcements!
The final point obscuring the mechanics is something I suspect is a bug: when a Chosen 'activates', they're allowed to summon reinforcements once their speech concludes even if they're out of action points. (This is another reason why I spent a while thinking summoning cost an action point, since I'd see Chosen walk into range, speechify, summon, and then do nothing else) Fortunately, it does have to actually be in their turn: if advancing your squad spots the Chosen, they don't get an out-of-turn opportunity to summon reinforcements.
Notably, this all means that Chosen replacing a pod is misleading, as the vast majority of the time they'll summon at least a pod's worth of reinforcements. Chosen thus don't generally depress corpse counts, and if you're slow to finish them they'll often actually inflate corpse counts across a run.
Also, while Strengths is for a later post, it should be explicitly stated that when a summoning Strength replaces this, the summoning Strength will still operate on the same mechanics, just with a different set of possible summons.
Anyway, returning to the topic of loot: the first time a Chosen summons reinforcements in a given mission, it's guaranteed one of the enemies summoned will drop loot when killed. This is true even if they summoned an enemy type that normally never carries loot, like Chryssalids, and is unrelated from the usual loot drop rate. So strictly speaking you should always endeavor to let Chosen have a turn, for maximum loot farming. This is slightly perverse, but in practice I mind it less than I first thought I would, as Chosen are sufficiently durable above Veteran that you're very unlikely to walk forward, 'activate' them, and then kill them with no chance for them to act, and so you'll almost never have an opportunity to go "I shouldn't kill them just yet". It does technically slightly encourage delaying hitting their Stronghold, but I mind that even less, given there's plenty of strategic mechanics discouraging trying to 'farm' them like that.
Interestingly, this guaranteed loot actually slightly inflates expected loot drop rates compared to the base game, as the game, regardless of version, tries to have at least one enemy carrying loot in every mission that isn't forbidden from generating loot, and this routine doesn't 'count' Chosen presence: thus, when Chosen jump you this usually means a minimum of two opportunities for loot. In practice, Vulture having been shuffled out of the GTS means you still have less loot overall in War of the Chosen; I'm actually curious if Vulture being made less consistently available is why this loot point is a thing. I actually historically thought Chosen summons having loot was a glitch, same as how baby Chryssalids sometimes spawning with loot is almost certainly a glitch, but Chosen summons are too consistent about it, and this is different from other reinforcements/summons: I find it unlikely this is some oversight where a general routine is applying that wasn't intended to.
In any event, Chosen summoning reinforcements is an important part of XCOM 2 experimenting with 'boss' enemy design, as it sidesteps one of the problems prior XCOM 2 boss enemies have suffered to varying degrees: that the situation is pretty binary. With a regular pod of 2-3 enemies, outputting a lot of damage, but not enough to wipe the pod, generally still results in a reduction in danger to your squad. (By killing 1-2 pod members) Knocking off 75% of the HP of a singular tough enemy is, in an immediate sense, the same as having done no damage at all. I honestly expected the Chosen to run right into this problem when I was first playing War of the Chosen, but them summoning reinforcements helps a lot, and indeed overall the Chosen tend to be safer to leave alive than their reinforcements -the reinforcements will be shooting to kill, where the Chosen actually don't.
Speaking of.
Merciful Cruelty
The Chosen will never directly kill a soldier in battle. Anytime a Chosen's personal, direct attack should kill a soldier, that soldier will instead go into Bleeding Out mode.
Note that I'm borrowing a different icon and making up an appropriate name: in-game, this quality is not listed anywhere, not even if you use mods like Yet Another F1 to look at a Chosen's abilities.
Also note that minions Chosen summon are not held to this, with this being particularly pertinent to the Warlock thanks to his Spectral Zombie summon spam: those will kill your troops just fine, as will his Spectral Lancers. So too will Mind Controlled troops murder your soldiers! Also note that SPARKs, being unable to go into Bleeding Out mode, get no protection at all.
My primary complaint with this quality is that the game doesn't hint at it at all. Among other points, this makes it non-obvious and a bit counterintuitive that generally good play involves focusing down other threats first, not the Chosen. I actually like that dynamic a lot more than, say, Alien Rulers horribly punishing you for trying to deal with other threats, but I imagine I'm far from the only player to initially think you needed to focus down Chosen first to avoid catastrophe.
My secondary complaint is that the Warlock is effectively not held to this mechanic, since firing his Disruptor Rifle is the only action he can take that it applies to, and he hates actually doing so, far preferring all his other tools.
My tertiary complaint is the suspicion that this is yet another deliberately invisible cheating-for-the-player mechanic in intent. It's tertiary though because I don't think it's an actually bad mechanic the way Aim Assist is.
Among other points, it actually makes a lot of narrative sense that the Chosen wouldn't be in a hurry to kill your troops. Their actual goal is to find and capture the Commander, and none of them cares all that much about eg ADVENT's infrastructure or the lives of the units you're killing. They're all also extremely confident in their skills, one might say overconfident, and the Assassin is the only one who isn't clearly indicated to literally toy with victims on the battlefield. I can buy they all are deliberately trying to leave your soldiers alive with intent to interrogate them and all. It'd be nice if they were actually capable of going after Unconscious soldiers, but given War of the Chosen's blatantly rushed state in general it's a bit hard to hold this particular, relatively minor, issue against the game.
I do appreciate that Long War of the Chosen went with this quality instead being a battlefield-wide modifier (That is, in LWotC a Chosen being present ensures any enemy landing a lethal blow always results in Bleeding Out) and the Chosen being able to kidnap Unconscious/Bleeding Out soldiers, as that's probably how this should've worked in the first place.
On a different-but-related note, I should point out that the Chosen will almost never target civilians in a Retaliation mission. It can happen, but I'm pretty sure primarily through edge-case AI-breaking confluences of events -for example, one of the handful of times I've had it happen, it was the Warlock having made contact with my squad and ended up with a SPARK as the only unit of mine in his sight. ie his only legal available hostile action was to take a shot, and his chance to hit the SPARK would've been a lot worse than to hit a civilian, between SPARKs having innate Defense and civilians effectively having negative Defense, leading to him choosing to shoot, then picking the target he was guaranteed to hit instead of the target he had iffy odds of hitting even though this meant he wasn't attacking an X-COM unit.
In practice, you can behave as if Chosen are no threat to civilians and almost never have it be wrong, in part because none of the Chosen has access to a damaging-by-default area-of-effect attack to potentially kill civilians while trying to target your squad. They all have access to at least one area-of-effect move, but not damaging ones.
Also note that, while the Chosen talk about about how they're going to kill your people when you do plot missions, that isn't a hint this mechanic is disabled: they still knock people into Bleeding Out in such missions. I'm honestly unsure if that's a result of War of the Chosen's general rushed state, or an example of flavor dialogue that was never intended to hint at mechanics.
Daze
Each Chosen has at least one way to inflict Daze. Daze is a complete disable on afflicted units, but can be ended prematurely for free by a unit getting adjacent to the Dazed unit, at which point they will have a free special action available to remove it, even if they have no action points remaining. (Disabled units can't perform this action: Dazed units cannot un-Daze each other) Clearing Daze always leaves the victim with 1 action point (Even if Revival Protocol or Restoration was used to clear it), and additionally has a 50% chance for them to become Disoriented.
One extremely bizarre point is that if you clear Daze manually, end up with a Disoriented soldier, and then clear the Disorientation with Revival Protocol (Or Restoration, I'd assume, though I haven't strictly tested this) the soldier will actually get back their lost action point. I suspect this is an error and the relevant code was supposed to do that when clearing the Daze with Revival Protocol, especially since it took me a while to stop mixing up Disoriented and Dazed -I wouldn't be at all surprised if the development team also found them overly-similar concepts/names. (I similarly haven't tested yet if Solace has this same bizarre behavior; this space will be updated when I remember to get to that)
Also bizarre -and frustrating- is that if soldiers are on slightly different heights, you can't do the Daze-clearing... even though the game will display as green such tiles, marking them as locations you can cure Daze from. Whoops!
Anyway, these mechanics might all make Daze sound not very threatening, but where Stun duration is usually 1-2 (And remember; Stun's 'duration' is 'how many action points it eats', not 'how many turns it eats'), Daze can have durations along the lines of seven turns. Even a short Daze is generally something like four turns. You're not waiting it out and ignoring it; you need to clear it.
On the plus side, Daze can also be cleared and blocked by the usual tools for dealing with negative mental conditions, such as Mind Shields or Solace, and killing the Chosen will immediately remove Daze from all your soldiers, no need to clear it manually.
Also note that Daze doesn't work on a SPARK, and the Chosen aren't coded to recognize that fact. The Hunter will happily waste his Daze grenade on a lone SPARK, oblivious to the fact that this does literally nothing. As far as I'm aware the Warlock won't make an equivalent mistake (I've never seen him try to Mind Scorch a SPARK), while the Assassin's two methods of inducing Daze will both do damage to a SPARK and so not be a waste of time, so this only really applies to the Hunter, but it can be helpful. More widely useful is that Mind Shields also block Daze, and the AI isn't coded to recognize that, either; the Warlock in particular can be made a laughingstock by fielding a squad of soldiers all equipped with Mind Shields, as he'll usually end up spending most of his time on useless Mind Scorches and also-useless Mind Control attempts, instead of shooting people.
Yes, this means you can cheese the Warlock pretty badly with Mind Shield spam. If you feel that's too exploitable and want mechanics changes, here's some mods you might appreciate: Mindshields Grant Resistance, which makes Mindshields +75 Will instead of immunity to mental effects, Mind Scorch Deals Damage, which will ensure the Warlock is at least doing damage while trying to inflict Daze, or A Better Chosen, which overhauls all the Chosen and really ought to be combined with the rest of the A Better (something) mods, but the relevancy is that it gives the Warlock an 'Overwhelm Mind Shield' ability to let him damage soldiers under Mind Shields and also makes him stop wasting his turn trying to do things to Mind Shield soldiers that won't work. (I kinda wish there was a standalone mod for adding in Overwhelm Mindshield and the 'don't waste turns' related behavior...)
Anyway, conversely, it should be noted that SPARKs cannot clear Daze like your other soldiers can. Don't waste time trying to have SPARKs get close to Dazed people; it won't help.
All three Chosen have a way to inflict Daze en mass, so clumping overly-much is a dangerous idea that can result in your entire squad being rendered helpless. Bondmates can make it less dangerous to clump (Stand By Me works even when disabled!), but the Assassin and Hunter both include knockback on their mass-Daze actions, so Stand By Me is only really reliable protection against Daze when fighting the Warlock in particular.
Daze itself might seem a bit odd a thing to put in given it's basically just a variation on Stun, but it really serves the purpose of setting up for two other universal Chosen abilities, starting with...
Extract Knowledge
The Chosen moves to a Dazed soldier somewhere within their full movement range and gains some Knowledge immediately. The Chosen promptly abandons the field of battle.
... this.
Here we come to the first actual point of the Daze condition: currently Dazed soldiers can be used by Chosen to gain Knowledge. Extract Knowledge raises the Chosen's Knowledge, which can be problematic in the mid-to-long-term, but in the short term performing an interrogation causes the Chosen to immediately leave the battlefield instead of sticking around to wipe your squad out entirely.
For the most part, Chosen can't inflict Daze and immediately follow up on it. Most Dazing actions provide no opportunity for the Chosen to leverage them the turn they were inflicted, such as by always ending the turn. Bizarrely, the Assassin's Harbor Wave is an exception, allowing her to mass-Daze your soldiers and immediately make off with Knowledge. She usually doesn't do it, but it's something to be aware of. Among other points, she likes to use Harbor Wave if two or more soldiers are lined up such that she can catch them both from her current position; try to not let your soldiers end their turn like that unless they're immune to Daze.


Strategically speaking, it's obviously bad to let the Chosen Extract Knowledge: optimally, you would never let the Chosen do this, especially since Chosen don't give bonus Ability Points if they leave on their own; a Chosen Extracting Knowledge is giving that Chosen a strategic boost and denying you a strategic boost! (Albeit a few Ability Points lost is pretty minor)
I'm emphasizing 'strategically', because on higher difficulties it can sometimes be genuinely better to let the Chosen Extract Knowledge in your first or sometimes even second encounter with them, as your early-game tools are very limited and what kinds of Strengths and Weaknesses they roll can potentially result in a situation where stubbornly preventing Extract Knowledge from going off actually results in a squad wipe. The Chosen won't directly kill (non-SPARK) soldiers with their immediate actions, but if all four or five soldiers are Bleeding Out, that still results in the squad wiped and a mission failed. You'll also lose any non-infinite gear they were carrying, of course.
Later in a run, you should virtually always have the tools to actually drive off Chosen, but those first few encounters? Extract Knowledge may be the less terrible option to arrange, and Chosen will virtually always go for it or its related ability if you give them the option.
Speaking of.
Kidnap
The Chosen moves to a Dazed soldier somewhere within their full movement range and kidnaps them, gaining Knowledge immediately, more than Extract Knowledge provides. The Chosen promptly abandons the field of battle. Until the soldier is rescued via a Covert Op, the Chosen will also gain more Knowledge than normal each month.
Kidnap is Extract Knowledge, except a lot more unpleasant to have happen.
Fortunately, initially Chosen will never Kidnap, in spite of what Lost And Abandoned might lead you to believe: leaving someone Dazed in the earliest encounters will result in Extract Knowledge happening, not Kidnap. They're not willing to Kidnap until Force Level 6 -basically, once you're seeing Mutons, ADVENT Mecs, and Advanced ADVENT Troopers spawning normally, you're either already at risk of a Kidnap or will be at risk very soon.
Anyway, as I noted in the Covert Op post, outside the special case of Mox in Lost And Abandoned, the game is really unreliable about offering the ability to rescue a Kidnapped soldier, to the point that you honestly might as well treat Kidnap as an instant kill; if a Sergeant or Lieutenant gets Kidnapped, it's entirely possible you'll beat the game without being offered a chance to rescue them, and even if you do get a chance it's entirely possible it'll be offered only very late, when you've got nearly a dozen Major-to-Colonel soldiers, where a Lieutenant is far too low-level to catch up before launching the final mission outside maybe abusing Promotion bonuses from Covert Ops. Indeed, a Kidnapping is often effectively worse than the soldier being killed, since their gear is taken with them, and if they have a Bondmate the Bondmate is trapped in a state of not being able to Bond with anyone while not being able to derive any benefit from technically having a Bondmate.
As such, you should generally endeavor to avoid leaving soldiers Dazed for even one turn past the early portion of a run: tactically, Kidnap is functionally an instant kill with no chance of failure, and strategically it's usually much worse than just having a soldier die. If you end up in a situation where you can't cure all the Dazes, you might want to prioritize saving soldiers with important gear (eg Alien Hunters equipment) and/or Bondmate status to minimize the sting.
Fortunately, the Assassin is the only Chosen who can and does inflict Daze turn after turn, and is also the only Chosen who can on-demand Daze as part of a damaging action: sacrificing soldier turns to clear Daze to avoid Kidnap going off isn't actually too terrible a cost most of the time, especially since Daze being inflicted by definition means any timer a mission has is stopped. Outside Protect The Device, Supply Extraction, Retaliation missions, and Chosen Avenger Defenses, Daze slowing the squad down is thus not too bad, and since usually the Chosen inflicting Daze means they didn't attack anyone that turn the action economy is generally to your favor.
This is all mitigated some by them summoning reinforcements, but that's a good thing in design terms! Reinforcements mean Daze isn't just a near-automatic waste of a turn on the Chosen's part. It would be really bad design if the Chosen regularly presented no threat to your squad at all.
Nonetheless, my point is that it's actually very tolerable to obsessively cure Daze to avoid Kidnappings happening, decent play should almost never result in a Kidnapping, and should also almost never result in anything else bad happening as a consequence of trying to prevent Kidnappings.
That said, on those missions that put you under time pressure without a timer per se being involved, you may find yourself forced to let a Kidnap go through, and even outside those cases it's possible to end up with the squad strung out. This is especially a concern if you're using SPARKs, since they can't cure Daze, making it easier to end up with a spacing that would be fine if all your soldiers were human, but whoops one soldier can only be reached by the SPARK!
So be aware of that if you have Shen's Last Gift.
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See you then.