Assassin of the Nightless City (Caster)

Assassin of the Nightless City (Caster)’s skills primarily circulate around her Noble Phantasm. Masters typically would use her first skill the turn they intend to have Assassin of the Nightless City (Caster) cast her Noble Phantasm, assuming the enemy is a boss or something going to stick around for a while. Her third skill would be cast on a later turn, particularly when the battle is turning well and the party needs a turn to heal and recover. Her first skill is a standard steroid with some boosts to party NP gain and is used turn one. Skill 2 is the only one that needs to be maxed, and should come first before general boosts of skill 1. Her 3rd skill is just healing in terms of scaling.

• Empress's Charisma (Summer) EX primarily gives the party buffs to their damage, boosting attack and Buster by small amounts. If paired with a Buster-oriented Servant they can gain from both of these, but the gain is so little it can in some ways be ignored for other Card-oriented teams. This skill does give the party a small NP gain rate boost as well, which could help for loopers in a team involving Assassin of the Nightless City (Caster). This skill can be safely left at level 9, and should be leveled 2nd.
• Ill-Fated Princess of the Wu Dynasty A has both a charge and Assassin of the Nightless City (Caster)’s best damage boost, against undead enemies. As this will apply to every attack in the wave by Servants in the party after Assassin of the Nightless City (Caster)’s Noble Phantasm, this should always be used right before Assassin of the Nightless City (Caster) casts it. This skill also does reduce the enemy’s charge by 1. As this is an NP charge skill that scales with level, it should be boosted to max first.
• Imperial Taoist Technique EX is a chance for the party to reset. Not only does it give the party a heal and take care of their debuffs, but it also will stun all enemies (assuming she’s turned them into undead already) so that the party can gain just pure health. Leveling this skill only raises healing amount by about 200 HP a level so it could probably be left at level 6 and leveled last. 

“If by any chance Master dies, I could now create an extremely rare Jiangshi Master.”

One would think having a sadistic desire to torture the living would be enough for one loli empress of China. But no, for as she matured into an older girl, she developed a further inclination to torture even the undead. As a support AoE Buster Caster she does quite an effective job at it, and even better when she gets other people to do her job for her.

Most of Assassin of the Nightless City (Caster)’s strength revolves around her Noble Phantasm, Come, Come, Cruel Jiangshis!. While at first glance this Noble Phantasm doesn’t cause too much damage to the enemies, its hidden bonus comes from inflicting the Undead Trait to all enemies for three turns. Once this trait is inflicted, she has a party-wide powermod granted from Ill-Fated Princess of the Wu Dynasty A and an on-demand stun from Imperial Taoist Technique EX. Besides her Undead advantages, she serves as a fairly good support as well thanks to party-wide bonuses from Empress's Charisma (Summer) EX.

Assassin of the Nightless City (Caster)’s main problem comes from her lack of personal damage. Her Noble Phantasm, despite being the strongest of all SR casters in terms of raw non-chance based damage, is still laughably weak compared to other classes. She also doesn’t have that powerful of a charge skill, locking her CE options behind them. Her endurance also is highly suspect, though some may consider that a benefit for her.

Assassin of the Nightless City (Caster) is a beautiful addition to a team as a Buster support against bosses and challenge quests. Through her undead trait infliction she can create a powermod situation against otherwise neutral enemies. She pairs especially well with Servants with built-in anti-Undead damage such as Martha Ruler Summer, Gray, and Scathach. At least, she will if her voice doesn’t torture you to undeath first! By the way, why is she Assassin of the Nightless City (Caster) instead of Caster of the Nightless City? Or even better we can just call her by her true name *Redacted*!

Turning Enemies into Jiangshi

The entire essence of Assassin of the Nightless City (Caster) comes from her ability to inflict undead trait for 3 turns to all enemies on her Noble Phantasm. This activates the instant she uses her Noble Phantasm, meaning any other Servant with the 30% buff from her second skill would get bonus damage from that moment forward. This is a Powermod bonus, meaning it would stack additively with Noble Phantasm damage boost and multiplicatively with other types of boosts. But it particularly shines when her allies have an Undead bonus damage boost in the first place.

Support

Assassin of the Nightless City (Caster) packs a particularly strong support kit. Her third skill comes with a debuff clear and a nice heal, keeping weakened Servants in the battle. Her first skill manages to give a sustained boost to Attack, Buster, and NP Gain, helping her allies through all waves.

Partywide NP Charge

Any Servant with a 20% party-wide NP charge with the ability to use a damaging Noble Phantasm of their own needs a mention as they can easily become a staple for some farming teams as a wave-clearer if using a properly strong CE.

Weak Damage

With mis-matched passives to her Noble Phantasm, Assassin of the Nightless City (Caster) has to rely on her weak party-wide steroid and her anti-undead damage to create more than laughable levels of damage. She does have a supereffective mod against Human attribute, but this only makes her borderline passing. 

Lack of Self-Charge

Sadly, Assassin of the Nightless City (Caster) doesn’t have much in the way of a self-charge, only gaining 20% from her party-wide 2nd skill. As early access to her Noble Phantasm is critical, she is pretty much bound to Starting Noble Phantasm Gauge CEs. 

Weak Defenses

Assassin of the Nightless City (Caster) has one of the lowest HP pools for a SR Caster in the game. Her skills don’t particularly aid that, lacking any form of hard evasion or defense. A couple of hits will likely take her out of commission. That said, this isn’t that bad of a thing as she is the type of Servant to give support and then is best getting off the field. Masters will need to be creative to get her taunted after her Noble Phantasm to remove her from the field. 

Assassin of the Nightless City (Caster) needs a starting gauge to work properly, as her entire point is to turn the enemy into undead creatures. As a result, Starting Gauge CEs work best for her. If a Master has other ways to get gauge to her like supports, then Taunt CEs are great to force her to exit the field. Her Max Bond CE may also find some niche usage to further boost Undead damage, but most likely it is best to aim towards a starting Gauge.

• Kaleidoscope / Great Marshal of Magic / Winter Crystal / Partake with the King / The Imaginary Element: At minimum, Assassin of the Nightless City (Caster) needs a 60% starting CE charge to function, assuming her 2nd append skill is leveled to max. With early access to her Noble Phantasm she can create the undead enemies needed for her support effects. Damage does not matter for Assassin of the Nightless City (Caster), so she can use any CE with a 60% gauge, but Partake with the King does give her a little extra damage. 
• Outrage / GUDAGUDA Poster Girl: Assassin of the Nightless City (Caster) has low defenses and is the type of Servant which best fires off her Noble Phantasm and skills and then gets killed. A taunt CE which can lead to her demise quicker is a great option for this, assuming masters have a way to boost her gauge through other Servants or Mystic Codes.
• Taoist Empress' Summer Vacation: As Assassin of the Nightless City (Caster)’s personal damage does not matter, her Bond CE can provide even further bonuses to her allies for undead powermod modifiers.