Spoiler Warning: Plot details follow. Read at your own risk.
Yggdrasil Core, known as Forest Cell in Japan, is the final boss of Etrian Odyssey 2 Untold: The Fafnir Knight's Story Mode or an optional post-game boss in Classic Mode, fought on the 5th floor of Ginnungagap.

This monstrous abomination, sealed deep within the ruins of Ginnungagap, is the final boss of the Story Mode campaign. The temple was built and the ritual of the Fafnir created, in order to keep this abomination sealed forever.

Yggdrasil Core (Etrian Odyssey 2 Untold) Edit

Yggdrasil Core
Yggdrasil Core
The calamity that was sealed for a thousand years. Its awakening is a destructive omen...
Enemy Data
HP 25000
AT 55
DF 40
EXP 200000
Skills Calamity Eyes, Cell Membrance, Armageddon, Poison Dust, Segment, Deadly Curse, Isolate, Core Charge, Root Cyclone
Items Demon Essence
Weakness All Attacks
Resistance Stun, Fear, Sleep, Panic, Paralyze, Head & Leg Bind
Immune Death, Petrify, Curse
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Similarly to Primevil, the Yggdrasil Core was born from High Lagaard's Yggdrasil Tree. Years of cleansing the planet of its pollution eventually resulted in the corruption of the tree's core component, turning it into a conscious, atrocious monster whose regenerative powers go far beyond that of mere mortals, and whose hunger knows no bounds. Should it go berserk, the destruction it would cause would be unspeakable.

Thus, a sealing ritual was created by the Black Guardian, a woman who lived in the Heavenly Keep and eventually founded High Lagaard. By sacrificing an individual of great life force, this person would become one with the Ginnungagap, turning themselves into a Guardian to maintain the seal

Driven by the same purpose of destroying the calamity and to free mankind from its threat, the Overlord, master of the Heavenly Keep and a member of the Yggdrasil Project, continued in his research for ages, trying to achieve the means to grant immortality to mankind. He was aided by the Black Guardian back when she still lived in his keep, but eventually, mankind decided to return to the lands bellow, leaving the Overlord alone to his research.

Core Irae
Enemy Data
HP 2500
AT 55
DF 60
Skills Land Slash, Demon Lance
Items None
Weakness All Elemental
Resistance Stun, Death, Petrify
Immune Fear, Sleep, Blind, Head & Leg Bind
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Ages have passed since then, and the ritual that has taken the lives of several heroes would go on until Arianna, the current princess of Caledonia, and her Knight, would be unable to complete the ritual due to complications and must, as a result, vanquish the Core for good. With the combined power borne from the research of the Black Guardian and the Overlord, they would finally vanquish the creature, putting an end to its threat.


Being the final boss of the story mode, the Yggdrasil Core is a very powerful and difficult enemy, so be prepared for a long fight. Bringing items that recover TP is important, as well as skills that target the entire enemy party. Having a variety of physical and elemental skills is also helpful.

Core Odium
Enemy Data
HP 4000
AT 50
DF 42
Skills Giga Fire, Freezing Nova, Thunder Rain
Items None
Weakness All Physical
Resistance Stun, Death, Petrify
Immune Curse, Sleep, Panic, Paralyze, Arm & Leg Bind
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At the start of the fight, the Core itself will be protected by a mental barrier, rendering it immune to all damage. In order to make it vulnerable, you must defeat its four appendages, two at a time. If you kill one but leave another alive, at the end of the next turn the Core will revive the fallen appendage with full HP, so be sure to kill them both at around the same time.

The first two appendages vulnerable to damage are the Core Irae, its tentacles. They both can use Land Slash to deal medium damage to a character row, or Demon's Lance, to deal medium damage that pierces across the front and back row. If you leave both alive for too long, the tentacles will together use Root Cyclone, which deals heavy damage to the entire party. They are weak to elemental attacks. They are also vulnerable to arm bind, which will stop all of its skills. While in this stage of the fight, the protected core will cast Poison Dust starting from the 2nd turn, which reduces the healing capacity of the entire party, and may poison them. Every 4 turns after this, it will cast Poison Dust again to refresh it duration.

After you destroy the two Core Irae, the two protuberant heads, called Core Odium, will become active. They will cast Giga Fire, Thunder Rain and Freezing Nova, elemental attacks that deal heavy damage to random targets, hitting up to 3 times. They are FAR more dangerous than the tentacles, as each head attacks with a different element, meaning you may not be able to protect yourself against both attacks, so make sure to kill them fast enough. Both Odium use attacks in the Fire - Ice - Volt cycle, with the left Odium starting with Giga Fire and the right Odium starting with Thunder Rain. The Odium are weak to physical attacks and are also vulnerable to head bind, which halts their skills. While in this stage of the fight, the protected core will cast Calamity Eyes two turns after the Core Odium become active, which remove buffs of a single target and may bind their entire body. Like with Poison Dust, it will cast Calamity Eyes every 4 turns afterwards.

Once you kill both Core Odiums, the Core itself will finally become unprotected, but will also start taking a much more direct role in the fight. The boss will open this stage of the fight with Deadly Curse, which lowers the maximum HP of the entire party and inflicts curse on them. This is dangerous, so make sure to heal the curse before you start attacking again, and remove the debuff with White Noble or a Unihorn as soon as possible. Yggdrasil Core will then start spamming Isolate, an attack that deals moderate damage to a target and splash damage to the adjacent characters. When it has been using Isolate for 7 turns or has been reduced to 75% HP, it will shift to its next attack pattern.

This next phase is signaled with Segment, which the Core uses to resurrect the Core Irae. It will then proceed to amplify the damage of one Core with Core Charge, followed by Calamity Eyes on the next turn. On the turn after, if any party members have debuffs, ailments or binds, it will spread these to the rest of the party with Pandemic. It then has a turn of inactivity before commencing the next phase.

The fifth phase of the fight starts with the Yggdrasil Core using Segment, this time to resurrect the Core Odium. The Core also protects itself with the mental barrier and removes all negative effects on it with Cell Membrane. Like the phase before, it will use Core Charge, Calamity Eyes, and then Pandemic, but the main threat of this phase is the Core Odium charging the main core's power on the Pandemic turn. Prioritize killing the Core Odium first, because on the turn following Pandemic, the Core will unleash Armageddon, a powerful almighty attack that gets even stronger depending on how many Odium were still around to charge it. After Armageddon, the core will repeat the pattern of Core Charge - Calamity Eyes - Pandemic - Armageddon, even if its limbs are destroyed, until it hits 40% HP. Even if it was reduced to 40% HP or lower prior, it will still go through this phase at least once.

The final phase is signaled with the Core using Deadly Curse one more time before proceeding to spam Armageddon every turn for the rest of the battle. Armageddon's attack power will increase each time the boss casts it, making it a race against time. Take too long to finish this fight and the damage will be impossible to survive, resulting in a certain game over. The boss will remain in this phase until it dies.

If you fight the Yggdrasil Core in the story mode of the game, the boss will have a second phase, where you will fight it solo with the Knight of Fafnir in his fully awakened form. Do not worry however, as the protagonist will be extremely powerful in this state, and it is nearly impossible to lose this fight, as you will have 9999HP and a powerful regen effect that will restore most of the damage taken.


Yggdrasil Core Edit

  • Armageddon (Uses Head): Massive almighty damage to the entire party. During penultimate phase, damage is based on number of appendages alive. During final phase, increases power for every casting instead.
  • Poison Dust (Uses Head): Inflicts poison and reduces the ability to recover HP of the entire party.
  • Segment (Uses None): Revives dead appendages.
  • Calamity Eyes (Uses Head): Removes buffs from a single target, lowers their defenses, and attempts to bind their entire body.
  • Isolate (Uses Head): Almighty attack to 1 target, with splash damage.
  • Core Charge (Uses Head): Increases the attack power of one appendage.
  • Deadly Curse (Uses Head): Inflicts curse on the entire party and reduces their maximum HP.
  • Cell Membrane (Uses None): Cures all debuffs, ailments, and binds to self, then protects itself with the mental barrier.

Core Irae Edit

  • Land Slash (Uses Arms): Medium Cut damage to the a character row.
  • Demon's Lance (Uses Arms): Line-piercing Stab attack.
  • Root Cyclone (Uses Arms): Heavy damage to the entire party. Requires both Core Irae to be alive.

Core Odium Edit

  • Giga Fire (Uses Head): Heavy fire damage to random targets. Hits 2-3 times.
  • Thunder Rain (Uses Head): Heavy volt damage to random targets. Hits 2-3 times.
  • Freezing Nova (Uses Head): Heavy ice damage to random targets. Hits 2-3 times.


  • Demon Essence (Worth: 12000 en)
  • None.

Conditional DropEdit

  • None.

Trivia Edit

  • Core Irae's name comes from the Latin hymn Dies Irae (Day of Wrath), where a trumpet call brings the souls of the saved to heaven while the rest are left to torment.
  • Core Odium's name comes from odium, meaning hatred.
  • Many of its attacks share their name with Primevil's skills. Its battle theme also shares the same name as Primevil's, With Much at Stake.
  • Like the Heavenbringer, it has a powerful almighty attack whose damage is based on the number of appendages alive.
  • Its body shape and overall appearance are similar to the Warped Savior.