Challenge Quest Summer 2019 Part 2 - Prison Break: DOG Police

Enemy Layout

Fatal Battle 1/1		311,030 DOG Police
		256,570 DOG Police
		173,560 DOG Police

[High Difficulty] Prison Break: Police Dog AP - 40

Drops	Spirit Root x1
Rewards	Morning Star x1

Boss Statistics

Avenger of Shinjuku
	HP	311,030
	LVL	55
	HP	256,570
	LVL	58
	HP	173,560
	LVL	60
	Class	Avenger
	NP Bar
	NP Type	ST
	Actions	Up to 3 per turn
	Traits	Male, Humanoid, Servant, Heaven or Earth, Wild Beast, Weak to Enuma Elish

Skill 1		Fallen Demon A+: Increase own Crit Chance (1 turn). Increase own DEF (1 turn).
Skill 2		Monstrous Strength B: Increase own ATK (2 turns).
Skill 3		One Cloaked in Death A: Decrease one enemy's Instant Death Resist (1 turn). Decrease one enemy's ATK (1 turn). Remove one enemy's buffs.
Break		Increase own Instant Death Success Rate (Unremovable).
Break		Increase own Instant Death Success Rate (Unremovable). Stacks with previous buff.
NP Effect		Frieren Scharfrichter: Apply Sure Hit to self (1 turn) first. Deal damage to a single enemy. Chance to inflict Instant Death on target. He will cast One Cloaked in Death on the target before using his NP! This means a target will no longer be protected if Invincibility/Evade buffs were active. However, Taunt will force him to use One Cloaked in Death on the Taunt Servant. His NP will still choose a random target afterwards due to the Taunt being removed. If he chooses a Servant with Invincible, damage is nullified, but note that there is still a chance that Instant Death activates.

Overview

Veterans will have a flashback to Shinjuku's Main Story, as Avenger of Shinjuku (ahem, DOG Police) is back to retrieve the convicts.
Unlike Shinjuku though, this version has less annoying Break Bar mechanics.
On each Broken HP Bar, DOG Police improves his Instant Death capabilities, thus increasing the odds a Servant will perish despite an Invincibility. Only guts can help a Servant survive from Instant Death.
The biggest problem in this encounter though, is DOG Police's Avenger class preventing easy access to class advantage. As such, he is remarkably sturdy while outputting high damage.
Meanwhile, DOG Police can strip buffs from a target and his NP cannot be easily stopped by Evasion, limiting defensive options.

Team Recommendations

BB is the only Servant with full class advantage, making her a powerful option in a full Arts team.
Avenger of Shinjuku does have exploitable traits, notably being male(Euryale, Orion, Medb) and a Wild Beast Servant (Cu Chulainn (Prototype)).
Alternatively, Berserkers are always an option, but DOG Police will deal extremely high damage to them while his Sure Hit can bypass many Berserkers only survival tool.
Lastly, a strong neutral non-trait option is always a viable option as well, but may take a bit longer.
Since his normal damage output is rather high, a defensive Servant such as Mash or a Taunt Servant can greatly increase a team's durability.
Expect Instant Death to actually activate after breaking his first Break bar. Consider using Taunts to distract DOG Police from potentially deleting your main DPS Servant.

Solo Potential

While this boss will be nerfed for the rerun (nearly halving his HP and reducing his level), Masters will be hard-pressed to find a good Servant that can actually solo this.

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.
Heracles remains a strong option with his bond CE, especially in combination with the Atlas Academy Uniform. See the video link for an example, ideally borrow one with grails/NP Upgrades.
BB can solo large chunks of his HP bar, but will need to have some Servants distract him to buy extra time.
Out of all 4 Challenge Quests with a copy of Ishtar on the line, this one is the most likely to require Command Seals to help with a solo run.
There is some RNG involved regarding buff removal from DOG Police or Critical Hits, success may require multiple attempts.

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.