Boss Guide: Ch26-2 (Atlantis)

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Enemy Layout

Poseidon Under Core
Auto Defense Unit Mk-2
Auto Defense Unit Mk-2
Poseidon Under Core
Auto Defense Unit Mk-2
Poseidon Under Core

Boss Statistics

Poseidon Under Core
Poseidon HP
Class Caster
NP Bar
NP Type
Up to 3 per turn
Divine, Super Giant
Battle Start 1 Energy Charge: Increase own NP Bar by an additional 1 bar every turn. [Permanent, Unremovable]
Battle Start 2 One Who Crosses the Starry Ocean: Increase own Damage to Servants with [Star] Attribute by 20%. [Permanent, Unremovable]
Break Intruder... Annhilate: [sic] Grant 1,500 Damage Plus to all allies (5 turns).
Break Deploy Defensive Device: Apply to self: 30% chance for Invincibility per hit (5 turns). [Unremovable]. (Each hit's probability is calculated individually).
Skill 1 Authority of Water A+: Clear debuffs from all allies. Apply Debuff Immunity to all allies (3 times, 3 turns). Recover all allies' HP by 10,000.
NP Trident Ocean Ray: Deal damage to all enemies. Reduce their NP Gauge by 20% and Remove 30 Critical Stars.


  • This is a relatively straightforward break bar boss encounter versus a Caster and three smaller Archer mobs (two of them start on the field, and the third will appear after at least one is defeated). The main gimmick to watch out for is the Invincibility break effect on the Caster boss's 2nd break.
  • The Poseidon Under Core will gain an extra NP bar tick each turn, and deals bonus damage against Star attribute Servants. Being a Caster with 5 NP bars, this means their NP will be ready in 3 turns instead of the usual 5.
  • On 1st break, Poseidon grants Damage Plus 1,500 to itself and all its allies.
  • On 2nd break, Poseidon gains a 30% chance to gain Invincibility with each hit for 5 turns. This can be circumvented using Ignore Invincibility skills.
  • Poseidon also has a skill that can clear all debuffs, grant 3-time/3-turn debuff immunity, and restore HP for itself and all allies by 10,000.
  • Poseidon's NP hits AoE, drains 20% NP Gauge, and drains 30 Critical stars.

Team Recommendations

  • Strong AoE DPS in the frontline and additional backup ST Rider DPS in the backline is a good idea.
  • Ignore Invincibility being available on the DPS will greatly improve the stability of the run, since otherwise on the 3rd HP bar, the boss has a 30% chance to have invincibility on a per-hit basis. Options include Francis Drake (even though she is Star attribute, the boss's bonus damage is only 20% so defensive class advantage is still applicable), Musashi Berserker, Xiang Yu, and Edmond Dantes (in the case of Dantes, save his invincibility skill for after 2nd break, since it only lasts 1 turn).
  • Damage / NP Gauge Support is useful to bring, with Waver, Skadi, and Merlin all being excellent options depending on the DPS's card color of choice.
  • Defensive Support options, particularly those with party-wide Evade / Invincibility options (such as Merlin) will help the party survive the boss's AoE NP.
  • Mystic Code: Chaldea Combat Uniform is useful for its Order Change skill, to bring backline support to help top off an NP Gauge. It can also be used to stun the enemy boss (provided it does not have the Debuff Immunity buff active), which can also help buy time.

Video Links

Quick Servant Suggestions

- Recommended
Ignore Invincibility DPS
Offensive Support
Defensive Support (Party-wide)
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