[Repost] "I pulled x Halloween unit +this -that. What do I do?"

In anticipation of the upcoming deluge of IV questions.

H.Kagero:
You need to decide whether you're going to go for a player phase, enemy phase, or dual phase build. I recommend player phase builds because she's a dagger so you can set up debuffs for your teammates, and she even comes with bold fighter.
Player phase build: barb shuriken, ignis/glacies (depending on whether you have higher def or res), death blow, bold fighter, armour march or atk wave, atk smoke or atk+3. See IV section for which refine to use.
Enemy phase build: double DD, vengeful, juice bottle. Refine your weapon to cover the defensive stat in which you don't have a boon.
Dual phase: DD or death blow, whichever phase you prefer to emphasize, bold fighter, QR. Not really my recommendation because other armours do this better.

I recommend against CC. You just spread yourself really thin. You take two hits with 43-ish HP and defenses in the mid 30s, and then you're done unless someone uses rehabilitate or recover+ on you.

IVs: +atk preferred for player phase builds; +def or +res preferred for enemy phase builds. Non-atk banes are nearly inconsequential on player phase builds. On enemy phase builds, -spd is best; -HP second best.

I recommend player phase no matter what IV you get for the reason I stated at the beginning.
-atk: makes enemy phase a little more attractive, but you still have 35 atk before anything else which is around the same as neutral Bartre so any matchup Bartre can win, she probably will also win.
+def or +res: refine your weapon for the same stat to increase special damage. I recommend this rather than atk refine because atk refine is subject to weapon triangle (which I guess you might want, in which case go for it).
+spd: maybe possible to do some funny anti-wary fighter kind of stuff with swift sparrow and a spd refine, but I would say it's unnecessary because you're almost certain surviving any counterattack so just accept it as a free ticket to debuff the opponent team.
+HP: doesn't really change anything, so proceed as normal.

Hyper-budget options: base kit, death blow 3 or even keep mirror strike, add iceberg and atk seal. Works with any IV including -atk.

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H.Mia: Pretty flexible unit. Res is not quite high enough to ploy unless you have a boon and add either res+3 in her A-slot or fortress res; offensive statline is ok but not especially threatening; def is enough to tank a hit due to middling HP for a healer. Nanna-like.

If you spam goad fliers you can get her atk into the 50s and her spd to the upper 40s, but you're better off with a proper mage for higher damage unless you want to pain+. If you want to use her as a colourless mage, she needs wrathful dazzle and either atk/spd bond (use flier formation seal) or atk+3 in the A-slot. The thing about putting her on a flier team is that flier teams often lean quite strongly to the player phase side and won't hesitate to take firesweep or desperation, so she won't be much needed for healing while a dancer will be very busy.

I tend to recommend her for a tactics team because tactics teams tend to be oversupplied on infantry candidates and undersupplied in fliers who wouldn't rather be on flier teams. She will probably give any two of the four tactics rather willingly in her C and S slots. With recover+ she doesn't even need the extra atk that much.

If you want her to tank, use fear+ and martyr+. Otherwise, anything goes.

In all cases, especially if you keep witchy wand, I suggest dazzling staff somewhere in the build. Cheapest is to use it as a refine. You won't get through armours in one round, so if you don't dazzle, they'll just vengeful double you and that won't work.

I also recommend miracle. Especially good if she eventually gets hit by an arrow.

IVs: not nearly as important unless you're using her as an offensive unit. She'll heal and inflict the user healer tricks (pain+, fear+, special shutdown) regardless of IVs thanks to dazzling staff.
-atk: consider keeping recover+, avoid trying to use her like a mage.
-spd: avoid trying to use her like a mage. Her A-skill still gives her a very reasonable amount of spd for defensive purposes.
-def: hurts her ability to survive one hit to her def, but if you keep her away from the front lines she'll generally be fine.
-res: my preference, to keep more physical bulk.
Again, any of these banes doesn't stop her from doing her job pretty normally.
+atk: still doesn't hit hard enough unless you spam goad fliers. Preferred boon for offensive builds.
+spd: very nice for survivability and for extra hits on the opponent to charge miracle faster; probably results in spd overkill if you have atk/spd bond and spam goad fliers.
+def and +HP: improves mixed bulk so that even the 40-atk armours with superboons won't OHKO her even if you don't use fear+.
+res: actually opens up the possibility of ploying if you take res+3 or fortress res in your A-slot.

Hyper-budget options: base kit, add dazzle refine on staff, live to serve 2 in B-slot, miracle, two buffs for the team. Hone atk might be especially good because the tank that repositions you out might like it against some tanky armour you just messed with. This build works for all IVs.

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H.Niles: a fun unit to build, with enough stats for player phase or enemy phase. Not recommended to try to go both ways.

Player phase: lots of weapons to choose from, and each requires proper support from other skills. The challenge is his low bulk for an armour, which will prevent him from taking more than 2 hits or sometimes just 1 unless you specifically build him to take additional hits. So he actually builds like an infantry bow in some builds.

Builds that will take only one hit (or none):
- firesweep + L&D + special fighter / bold fighter + moonbow
- fishie bow + swift sparrow + special fighter + moonbow
- fishie bow + swift sparrow + special spiral! + iceberg/luna (use on a tactics team with L.Hector. In your first round, you have a 2CD special which will activate on doubling, and from there on it's a 1CD special in desperation).
- any typical infantry build using slaying bow + desperation: flashing blade iceberg/luna, for instance
- any typical infantry build using shining bow + desperation: flashing blade moonbow, for instance

Builds designed to tank counterattacks:
- shining bow+def, brazen def/res, special fighter, glacies
- slaying bow+def, swift sparrow, special fighter, aether

On any player phase build, he would like to have armour march, but if you can't give him armour march then ward or fortify armour will do, or if you have +res and refine his bow for res, spd or def or atk ploy are also options.

Enemy phase builds:
- DD9 (guard bow+def, distant def, vengeful fighter, distant def seal, iceberg because he's so fast the enemy might not double)
- if you have enough spd already (ex: from a boon), you can consider stuff like slaying bow+spd or +def, CC, special fighter, aether, close def

IVs: +atk or +spd preferred for player phase builds; +def preferred for enemy phase builds.
+HP: doesn't really change anything. Proceed as you otherwise would.
+res: opens the door to ploys if you use a res refine on his bow, which can be convenient because 35 res will ploy almost any fast unit in the game and the most notable exceptions are fliers (Caeda, Clair, who might use fury and have >35 res)
-atk: means you probably have either more spd or more bulk, both of which are good for special fighter builds. If you experience issues with damage, choose a build involving a 4-charge burst special.
-spd: use bold fighter or an enemy phase build, or buff his spd. He still has 36 spd with a bane, which is equal to neutral LA Lyn and faster than neutral Cordelia, Soleil, and Sothe and is entirely usable for player phase builds. With hone armour he's up to 42 spd without a weapon refine or A-skill, so he's definitely still in business.
-def, -res, -HP: of little consequence in player phase builds
For clarity, +def -atk will still work for player phase builds using builds such as shining bow+def + brazen def/res + special fighter + ignis, or if doubling becomes an issue, bold fighter + bonfire. +def -spd will take a vengeful DD9 build easily or you can play the same brazen def/res build I just suggested using bold fighter.

Hyper-budget options: without -spd, refine his bow for spd, get desperation 2 from a 4* Mae, add ward or fortify armour and atk or spd seal. Moonbow might be the special of choice. With -spd, could still work if the seal is spd+3, or you can do some QR thing with the distant def seal and something like mirror stance 1 from a 4* Silvia.

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H.Myrrh: very straightforward unit. Statline and rest of the kit screams "gimme DC." Other options for A-skills: armoured blow to try to force more doubles, death blow, sturdy blow, close def, breath skills (especially warding, to cover slightly lower res).

Seal options: her res puts her in an interesting spot if you're using DC. Green and some red mages will die in one hit, while blue mages have her crushed, so you might not bother with distant def. Close def maybe doesn't help that much with manaketes because they tend not to hit as hard and in any case the real killers are the Tikis who might OHKO her even through close def. If you don't use DC then distant def might be good for covering those times when she'll need to bide fire from mages.

IVs: if you like arena score, +atk is preferred; if you don't care, prefer +def or +res according to taste. Most people would recommend -spd and it's a good option; I personally tend to prefer -HP because I have -spd on Dorcas (exactly the same spd) and it actually does make a difference sometimes, and it can be helpful to take one less hit because slow units usually have pretty good atk and you're getting a bonfire out anyways and backing it with 54 atk targeting res (or whatever is lower on a ranged unit).
+HP: good for panic ploy. Other than that, doesn't really change anything.
+spd: you could try to be cute with something like spd/res bond and avoid doubles from slow mages and manaketes. It's legit vs someone like Lilina, actually, especially if you're outmerged. You don't want to get hit twice with nearly 70 atk. But even without the bond you might keep up with the slow mages including Deirdre (28 neutral, so she'll double you if you don't have a boon or OHKO her back) if you don't get spd ployed. So just enjoy being able to avoid doubles from slow units. Like I said, they tend to hit pretty hard.
-atk: may cause issues on player phase if you use a 4-charge special because it's not going to activate. 51 atk targeting a unit's lower defensive stat will often do the trick, but if you find that you have issues, use death blow, buff her atk, or switch to moonbow (maybe glimmer in PvE).
-def: annoying. Might add value to armoured blow.
-res: makes her res more iffy, but if you're using DC the situation hasn't changed where she'll OHKO a lot of mages who attack into her if they're not blue, and nothing has changed against blue mages. So now we're left with manaketes, in which case close def seal might be a good idea.

Hyper-budget options: base kit, armoured blow, def+ seal. Switch to ignis or moonbow, depending on whether you want to focus on player phase or enemy.