Return of Nero Fest 2018: Act II - Master and Pupil of Light and Shadow

Boss Statistics

Scathach
	HP	518,875
	LVL	90
	Class	Lancer
	NP Bar
	NP Type	ST
	Actions	3 per turn (acts 2x per turn when Cu is alive)
	Traits	Humanoid, Female, Servant, Weak to Enuma Elish, King

Passive		Passively high crit chance.
Passive		Increase debuff resistance by 20%.
Skills		Upon entering the third wave, Scathach will auto-cast a skill that inflicts the NP Seal debuff on your entire front line for 3 turns. This can be removed with debuff cleanse skills.
		When Cu falls, at the start of the next turn, Scathach will cast Revenge of Dún Scáith, which instantly kills all party members (Guts will still work, but dodge/invuln does NOT work), and grants herself increased damage, crit chance, crit damage, and a chance to inflict instant death on every hit. Note that she will prioritize using her NP over this skill if her gauge is full, and will not cast this on the same turn as her NP (she normally uses her NP > Evade skill > Auto attack). In cases where she does her NP instead, she will delay using this skill until the next turn. Caution! On rare occasion, Scathach may choose not to apply her Evade skill, in which case she will cast Revenge of Dún Scáith on the same turn as her NP (NP > Auto Attack > Revenge of Dún Scáith). Be wary of using this method to avoid the skill as it is not guaranteed.
		Grant self Evasion (1 turn) and 80% chance to increase crit chance up and/or crit damage up (3 turns). She uses this skill randomly when Cu is still alive and will use it every turn when she is the last one standing.
NP Effect		Gae Bolg Alternative: High single target damage with a high chance of instant death and a virtually guaranteed stun.

Cu Chulainn
	HP	306,976
	LVL	70
	Class	Lancer
	NP Bar
	NP Type	ST
	Actions	3 per turn (acts 1x per turn when Scathach is alive)
	Traits	Humanoid, Male, Servant, Weak to Enuma Elish, Divine, Brynhildr’s Beloved, Heaven or Earth

Passive		Increase debuff resistance by 15%.
Skills		When Scathach falls, at the start of the next turn, Cu will cast Revenge of Dún Scáith, which instantly kills all party members (Guts will still work, but dodge/invuln does NOT work), and grants himself increased damage, crit chance, crit damage, and a chance to inflict instant death on every hit. Note that he will prioritize using his NP over this skill if his gauge is full, and will not cast this on the same turn as his NP. In cases where he does his NP instead, he will delay using this skill until the next turn. Caution! If his Evade is still active, then he may still cast the instant death skill on his NP turn as he no longer will spend a turn using Protection from Arrows.
Skills		Grant self Evasion (3 times) and DEF up (3 turns). He uses this skill randomly when Scathach is still alive and will use it every turn when he is the last standing.
NP Effect		Gae Bolg: High single target damage, reduces target’s DEF (3 turns), with a chance of instant death.

Battle 1/3	23,980 Werewolf	24,014 Goblin	23,980 Werewolf
Battle 2/3	44,567 Goblin	44,567 Goblin	27,463 Werewolf
Fatal Battle 3/3	518,875 Scathach		306,976 Cu Chulainn

Boss Analysis

Scathach will auto-cast NP seal on your entire front line (lasts 3 turns) right as the third wave starts, which cannot miss (500% success rate) unless you have debuff immunity () on. This can also be removed using Servants’ cleanse skills, or the debuff cleanse skill on Mystic Code: Atlas Academy Uniform.
If Scathach or Cu is killed before the other, the remaining member will cast Revenge of Dún Scáith on their next turn that causes guaranteed instant death to your entire front line, while buffing themselves with damage up, crit chance up, crit damage up, and a chance to inflict instant death on every hit. Guts will allow you to survive the instant death skill, but Evade and Invincibility do NOT work. They will still use this skill even if they are inflicted with the Skill Seal debuff.

Cu Chulainn using Revenge of Dún Scáith when alone and Skill Sealed.

When either Scathach or Cu are alone, they will spam their Evade skills every turn. You can either remove them with Buff Removal skills, or utilize Sure Hit / Ignore Invincible skills. Buff block skills (such as Jeanne Alter’s NP) can also prevent Evade skills from succeeding on a subsequent turn. Otherwise, leave Cu for last as his 3-hit Evade can be broken with Extra chains
Cu has a shorter NP bar than normal. Delaying his NP so it syncs up with Scathach can make surviving their NP turns a lot easier.
Since both opponents become immensely threatening after becoming the last one standing, try to eliminate both of them simultaneously. You will need to whittle down their HP relatively evenly through AoE NPs and/or by switching targets between both of them with various attacks. Expect both of them to use their Evade almost every turn.
It is possible to postpone the instant kill skill by eliminating one of them on the same turn the other one’s NP gauge is full. The remaining one will use their NP on their next turn instead of the skill (the skill will be used on the following turn instead), buying precious time. Caution: If Cu is left as the last standing and already has his Protection of Arrows active, he is more likely to use Revenge of Dún Scáith even on his NP turn (normally he will NP > Protection from Arrows > Auto Attack, which becomes NP > Auto Attack > Revenge of Dún Scáith if his Evade is active). Sometimes on rare occasion, they may choose not to apply their Evade skill even if it isn't active, in which they will use their NP > Auto Attack > Revenge of Dún Scáith.

Team Composition Recommendations

AoE Saber options are especially attractive since they help to balance the damage between the two enemies without accidentally killing one of them before the other, while at the same time receiving half damage due to class advantage.
Buff stacking on your AoE Saber to deal as much damage as possible to the bosses simultaneously is a good option. When selecting damage support Servants, note that buffs of different types, such as attack buffs, NP damage buffs, and card type (Arts/Buster/Quick) buffs stack multiplicatively, while same type buffs only stack additively. As a result, if your damage dealer does not have a Buster buff (Altera), bringing a support with a Buster buff would be more effective than stacking additional Charisma buffs. Some buffs have much stronger effects though, so look at both the added percentage and the type.
Most Masters will have to chip away at the HP of Scathach and Cu first to be able to finish them off with their NP. For Masters who bring support Servants, a non-damaging NP is excellent for leaving Cu with only 1 hit left on his Protection from Arrows. This can be used to great effect to set up damaging turns or the final killing blow(hit him once before firing off the NP).
To deal with the 3-turn NP Seal inflicted at the start of the match, bring a Servant with a debuff cleanse skill or use the Mystic Code: Atlas Academy Uniform.
To deal with Evade spam, bringing Servants with Sure Hit / Ignore Invincible, Buff Removal, or Buff Block are all possible options. The Princess of the White Rose CE should still be equipped on the main dealer, but including one Sure Hit CE in the backline can be useful to finish the encounter.
Since both Scathach and Cu have single target NPs, Servants with a taunt and Invincibility/Evasion skill are great options if more time is needed to chip their HP down for the kill. Since Cu has a shorter NP bar, try to delay him to taunt both NPs in one turn.
Mystic Code options are flexible. If you do not have a Servant with a cleanse skill on hand then Atlas Academy Uniform is recommended for the debuff cleanse skill. For buff stacking, the Chaldea Combat Uniform is preferred in order to bring in more buffs from the backline. For Buster Servants, the Anniversary Blonde Mystic Code is also incredible for finishing off Cu and Scathach in one final turn.

Budget Strategy Recommendations:

Whatever you do, make sure to charge and prepare for the final wave by abusing the first two waves of opponents. Starting with a 100% charged NP is ideal.
Among the AoE Sabers Mordred has the most balanced kit for tackling this Challenge Quest. Because she has her own debuff cleanse, more Mystic Codes can be used while her upgraded NP does impressive damage. Mordred is the ideal candidate to stack buffs on and can even potentially defeat the final wave in one NP with enough buff stacking and a Limit Broken Two Gods Three Legs.
However, any of the DPS Sabers listed carry enough damage to clear the encounter by first chipping away at their HP pools before blasting them with one final NP. Try and select the (support) Saber with the highest NP upgrades, grails and skill levels.
Ryougi Shiki is the odd Saber out, as she trades high damage for both Ignore Invincibility and incredible amount of staying power with her massive heal. A steady Arts-based option.
For Masters with one of their own SSR Sabers (or Altria Pendragon Alter), borrowing a support like Merlin, Waver or Nightingale to further improve their damage is a great idea. The shorter this Challenge Quest lasts, the better.
Saint Martha (Rider) is an excellent option for Masters without access to debuff cleanses. Consider borrowing her to free up your Mystic Code and stack more buffs. She can also reduce defense by up to 30%( or 50% with NP) and remove the annoying Evasion buff.
Most of the top AoE Sabers are actually Dragon trait Servants. Jeanne d'Arc (Alter) can be used to great effect here as a secondary attacker by applying buff blocking with her NP and an up to 40% Charisma attack boost to her dragon allies.
Chevalier d'Eon can soak up damage for a truly impressive amount of time and the defensive Servant of choice to buy time to chip away at the enemy's HP pool. Mash is no slouch either once again.
If Cu is the last one alive, Nero can do a powerful last stand with her Thrice-Setting Sun skill. Try to equip her with one of the various Sure Hit CEs.

Soloable for New Masters?

Certainly! Although Masters need to be clever about stunning Cu or Scathach when they unleash their damage to prevent them from casting Revenge of Dún Scáith.
When soloing, Masters field lvl 1+ Servants with a Taunt (Georgios and Leonidas) to draw fire for 2 turns (one at a time) and then leave the borrowed maxed Servant on their own.
Mordred's self cleanse (for the NP Seal) and sheer damage makes her an excellent option to destroy Scathach on the first turn, while Cu is stunned from a Gandr from the Chaldea Combat Uniform.
Masters can try to chip them first, but the strategy would be reliant on either of them not casting Evasion too often (which of course they will).
Try and look for grailed or NP Upgraded Sabers to make life easier.

Video Links

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.

Team Recommendations Table

Class advantaged DPS options with Debuff Cleanse/Immunity

Other DPS options - AoE Sabers

Anti-Evade Options – Sure Hit / Ignore Invincible

Anti-Evade Options – Buff Removal
	Strengthening after NP
Anti-Evade Options – Buff Block

Support – Debuff Cleanse on skill (for NP Seal)
	Strengthening
Support – Taunt + Invincibility during NP turns

Support – NP Charge and Damage Support

Support – Damage Support (Buff Stacking)
	for Dragons Buster Arts