Revival: Summer 2019 Part 2 - Challenge Guide: Bull of Heaven

• The proper Challenge Quest for the entire Summer 2019 Event, this showdown against the Bull of Heaven pulls no punches and ranks amongst the harder Challenge Quests released so far. It remains unchanged from the original run.
• This is a very heavy fight against a massive Rider opponent with Ishtar's initial Archer class showdown deterring easy full Assassin compositions. 
• Ishtar is highly dangerous, dealing high damage, capable of charging her NP, and potentially granting herself Invincibility at very inopportune times. She is often to prone to casting Shining Majestic Crown at low HP. 
• The Bull of Heaven itself is a fearsome opponents, dealing high ST damage, but immense AoE Damage on Critical Hit, which as a Rider it is very prone to down.
• Its Rider class also puts a damper on most standard Caster support compositions. Casters can be used, but will fall sooner rather than later. 
• In addition, it's most annoying habit is removing the buffs off one Servant, often stripping valuable protections and causing that Servant to perish if not protected anew. It will always remove all buffs from the team on its first Break, which often coincides with an NP turn, so beware.
• Its Noble Phantasm is not immediately lethal, but adds up quickly with its normal AoE attack damage. In addition, the skill/NP seal it can inflict can slow down the skill rotation potentially leaving the team unprotecred. 
• However, both Ishtar and the Bull of Heaven are Divine. The Fondant Au Chocolat Craft Essence with Anti-Divine capabilities is extremely effective here.

• With all the common Caster Supports suffering Class Disadvantage versus the Bull of Heaven, creating a strong team composition is much more difficult. 
• In addition, Ishtar is an extreme threat early on, and has to be removed from combat ideally before she can even launch her NP as she will unleash massive damage on any fielded Assassin Servants.
• Thus fielding a strong ST Lancer or Berserker with Starting NP Gauge (unleash the Kscope) to remove her from play immediately is highly recommended. 
• Assassins have to pick up the offensive slack, as the Bull of Heaven's high HP and AoE damage potential does limit the viability of Berserker Servants.
• Assassins with powerful sustained offense and strong durability are especially powerful here, with First Hassan providing a suitably impressive performance.
• Furthermore, with Casters out of the picture, Mash, Jeanne d'Arc, and even BB are excellent substitutes for defensive back-up with Jeanne providing the teamwide AoE Invincibility Merlin is hard-pressed to provide here. 
• A stalling-oriented Master can field a full Arts team with Mash/Jeanne and an Arts Assassin of their choice. 
• Fondant Au Chocolate, the Event CE from Valentine 2019, is one of the strongest options for the main DPS, but anti-Divine Servants also receive a performance boost. 
• Critical Chance Down also gains a rare moment to shine. The Bull of Heaven only launches its AoE Attack on a Critical Hit. Preventing its Critical Hits via Critical Chance Down is rather effective at reducing overall incoming damage. Many Assassin Servants such as Carmilla, Emiya, Jack and Hassan of the Hundred Personas are capable of providing the debuff.
• The Atlas Academy Uniform Mystic Code is powerful here, with its cleanse providing key buff removal after an NP from the Bull of Heaven or before launching an NP with a card demerit. The cooldown reduction and Invincibility are also valuable tools to either protect key members or support First Hassan's solo rampage.
• If the encounter is proving too difficult, First Hassan can solo half the encounter by himself even at lvl 90 NP1. Activating a full party ressurection via Command Seals with First Hassan while the Bull of Heaven is on his last Break bar ought to be enough to clear the encounter.

Some summarized (Friend) Support picks:

• First Hassan is the pick of choice if your roster lacks a strong Assassin to rely on as he functions incredibly well as is.
• Jeanne d'Arc is the Support pick of choice if your roster contains a strong Assassin/Arts DPS option.
• Masters who own Jeanne d'Arc can instead borrow a strong Arts Assasin.
• Mash is always a good third slot for general survival.
• Caster support is viable, but very fragile. The sheer offense someone like Merlin provides is still good enough for (veteran) Masters to blast through the encounter.

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.

• First Hassan NP5 lvl 100 full Solo with Fondant Au Chocolat (17 turns).
• Shiki (Fondant au Chocolat) comp with Mash and Jeanne (MLB Prisma Cosmos) - Stable and sustained offense (30 turns).
• Hassan of the Hundred Personas (Fondant au Chocolat) comp with Mash and Jeanne (MLB Prisma Cosmos) - fairly stable/slow and shows defensive power (55 turns).
• Hassan of Serenity/Cu Chulainn/Jeanne (MLB Prisma Cosmos Support) comp that turns into a remarkably stable Mash/BB/Jeanne Arts stalling team - 63 turns.
• Low Rarity team with Diarmuid/Mozart/Mash/Hasan of Serenity/First Hassan(borrowed, NP2)/Hans. Devolves halfway into First Hassan solo (28 turns).