Boss: Raining Encounter - Ryougi Shiki (SERAPH)

• As general Challenge Quests go, this fight is more in line with the rest of the event in terms of difficulty rather than a huge step above. The Instant Death mechanics can be highly unpredictable though. 
• 1st Form NP Charging: Ryougi Shiki’s Assassin form is a lot more dangerous than her Saber form due to her self-charging skill and low NP gauge. If not taken out quickly enough she will promptly take out any team member with the unpredictable timing of her Noble Phantasm.
• Hefty BB Slots Debuff: The BB Slots for this fight inflict a heavy 50% NP damage down on the frontline at the battle start and lasts indefinitely. However, since this does not affect the backline, Masters can bypass it by putting the main damage dealer in the backline and switch them out with Chaldea Combat Uniform. Or they can cleanse it of course. 
• Critical Onslaught on Break: Shiki will cast a powerful Increased Critical Hit Chance Buff on herself upon switching to her Saber form. This critical buff cannot be removed in this version of the encounter.
• NP Bar Progress Carries over on Break: Shiki will not be deterred by a broken HP bar, and if she is ready to NP in her Assassin form, she will NP in her Saber form right away. Try to avoid this as her Saber form will have a chance to Instant Death the entire team! If Shiki is close to NP'ing around the time her bar breaks, let her Assassin form cast it. 
• Instant Death Roulette: As both forms’ Noble Phantasm can indirectly bypass Invincibility thanks mainly to their chance of applying Instant Death, Masters are at the mercy of the Random Number God when it comes to surviving their NPs. Masters should principally aim to tank the damage with the standard survival options and hope for the best, but guts effects allow any affected Servant to survive any Instant Death attempts. 

• Team Composition: Masters can still field the standard Challenge Quest composition consisting of multiple Supports and 1 or 2 damage-dealers with a final last-stand-Servant. However, to avoid messing too much with Instant Death mechanics, try to focus more on offense rather than defense and minimize the amount of NPs she can fire.
• Mystic Code Choice: Consider abusing Order Change or the Atlas Academy Uniform to nullify the effects of the BB Slots.
• Abusing Class Advantage: Alter Ego and Berserker Servants are the only ones that have bonus damage against BOTH versions of Shiki, so they are good catch-all damage dealer. Otherwise, bringing both a Caster and an Archer(potentially in the backline) for each version respectively, is also a valid choice.
• Anti-Trait Alternative: Anti-Female Servants are also decent substitutes for Masters without viable Alter Egos / Berserkers. Similarly, Servants without bonus damage but possessing extraordinary neutral damage across several turns are also notable alternatives.
• NP Draining: Due to the Assassin version having both a 3-charge NP gauge and a skill that charges her gauge by one upon casting, NP Drains and NP Seals are highly effective tools to buy more time before an NP comes out. 
• Evasion: Assassin Shiki can be difficult to kill quickly as she uses her Evasion liberally. Consider bring CEs or Servants with Sure hit and/or Invincibility Pierce. 
• High Offense Alternative: High Damage setups that can destroy her Assassin form quickly will help make the fight more predictable and easier to manage.However, note that the Saber form is also dangerous in her own way if she does get to NP. 
• Guts: Servants that have multiple Guts status buffs are fantastic as the Last Man, as they can counter Shiki’s Noble Phantasm quite effectively. Irisviel can also prevent any surprise deaths with her teamwide guts buff. 
• Taunters are a very effective way to tank the Noble Phantasm from Assassin Shiki, effectively protecting the main damage dealer from any Instant Death shenanigans.

Note that these videos are not affiliated with GamePress, but showcase some lineups that are effective in clearing the final challenge. These can serve as a good reference for how to rotate skills during this quest or simply to have a look at the encounter before diving in.

• Zhuge Liang + Tamamo no Mae + Sanzang / David team
• Low Rarity Setup with Leonidas / Caligula / 2x Andersen / Arash and Angra Mainyu
• Meltryllis + 3 Taunters
• Double Meltryllis support with Arash to bring them out from backline
• Arts Offensive setup with Chloe von Einzbern as main DPS