Spoiler Warning: Plot details follow. Read at your own risk.
Before you squats an abomination born from your most terrible nightmares. The monster dwelling in those blood soaked depths must be the labyrinth's final enemy! Unsheathing your weapons, you prepare to face the heart of the labyrinth!
Yggdrasil Core introduction, Etrian Odyssey

Yggdrasil Core.

Yggdrasil Core (Primevil in first installment) is the true final boss of the first Etrian Odyssey game and its remake.

It can found in the B30F (The sentinel of eternity), the final floor of the Claret Hollows, and is the hardest boss in both games it appears in. It is by far one of the most powerful entities in the entire series.

This abomination is the sentient Yggdrasil Tree's core, the last stand of the labyrinth. It has many forms of attacks, having control over the three elements to cast devastating, lost spells, or using its long tentacles to rip apart unlucky explorers. Should one survive those attacks, it can devastate its enemies in other ways too, using hallucinating pollen to destroy the mind, or using its powerful magic to rot its victims alive, leaving nothing in its wake.


Primevil ending

Primevil as seen in the ending movie of Untold

In Etrian Odyssey, very little was revealed about Primevil. The only known fact, revealed by the Bestiary Entry (or Monstrous Codex), was that Primevil is the heart of the Yggdrasil Tree.

In Story Mode of Etrian Odyssey Untold, its backstory is expanded and elaborated upon. Renamed as the Yggdrasil Core, Primevil is confirmed to be the main part of one of the seven mighty trees, created during the Yggdrasil Project, a project in which scientists had tried to create something meant to purify the world, absorbing all the pollution so that mankind could live properly again. The trees managed to succeed in their original task. However, due to the enormous amount of pollution absorbed by it, their cores would eventually mutate and become unstoppable monsters. They had hypothesized this, and thus Frederica Irving offered to be shut inside a capsule that would awaken her exactly one thousand years later. 

In the meantime, various other failsafes were prepared - Gungnir units, which are designed to destroy the Core at the cost of literally everything in its vicinity. The town of Gotham was subject to one such unit and was thoroughly annihilated. M.I.K.E., the AI overseeing Etria's Gungnir unit, was hellbent on activating the Gungnir, and turned against the party when they suggested an alternative means of destroying the Core without sacrificing Etria. The party eventually obtains the Yggdra Virus, a special countermeasure developed by Visil as a last-ditch effort to weaken the Core enough for them to defeat it.

Primevil (Etrian Odyssey) Edit

Primevil fix
The Labyrinth's core which erected the Claret Hollows to protect itself.
Enemy Data
HP 90000
AT 585
DF 170
Skills Cyclone,Slash,Rush
Items Demon Core
Weakness None
Resistance None
Immune Status Ailments, Binds
This box: view  talk  edit

  Primevil is the final boss of Etrian Odyssey. Not much has been revealed about it; in fact, the only known detail is that Primevil is the core of the great Yggdrasil Tree. Before you can fight it, however, you must have killed the Wyrm once; the beast has a seal on the door that leads you closer to Primevil, which can be unlocked once you defeat it.

Although unnecessary, it is recommended that you also defeat the Dragon and the Drake, as one has sealed a door leading to a healing fountain and the other has sealed a warp area, which would allow you to travel freely from the Stratum entrance to B30F.

Once you step through the Wyrm's unlocked door, you will have to face weaker clones of the three elemental dragons; DrakoidDragoid and Wyrmoid in the aforementioned order. You cannot head back once you enter, with the exception of using a Warp Wire.

You may finally battle Primevil after defeating the three clones.

Skills Edit

  • Necrosis (Uses None): Instant death attack on the whole party, high chances of working. Very dangerous, can easily cause a instant Game Over if your party lacks death resistance.
  • Explode (Uses None): Extremely heavy, fire based damage.
  • Frigid (Uses None): Extremely heavy, ice based damage.
  • Storm (Uses None): Extremely heavy, thunder based damage.
  • HP Up (Uses None): Strangely, this attack does nothing, skipping a turn.
  • Entangle (Uses None): Binds all body parts of the whole party. Extremely dangerous if your buffs are about to vanish, rendering you defenseless against the boss' powerful attacks.
  • Pollen (Uses None): Inflicts random status ailments to the whole party.
  • Smash (Uses None): Deals heavy crush based damage to the whole party.
  • Slash (Uses None): Deals very heavy, slash based damage to one target. Hits four times in a row. Very powerful, may kill even with defense buffs.
  • Rush (Uses None): Deals heavy, pierce based damage to random targets. Hits up to 6 times in a row.
  • Resolve (Uses None): Remove the buffs of the whole party. Used if your party has at least 10 buffs.

Drops Edit

  • Demon Core (Worth: 18000 en)
  • None.

Conditional Drop Edit

  • None.

Yggdrasil Core (Etrian Odyssey Untold) Edit

Yggdrasil Core
Yggdrasil Core
The Labyrinth's core, which erected the Claret Hollows to protect itself.
Enemy Data
HP 90000
AT 99
DF 75
EXP 999999
Skills Land Slash, Activate, Armageddon, Segment, Demon Rush, Explode, Freezing, Thunderstorm, Root Cyclone, King's Resolve, Necrosis, Ancient Pollen, Entangling Ray, Cell Membrane
Items Demon Core, True Demon Core (Conditional Drop)
Weakness Fire, Ice, Volt
Resistance Sleep, Blind, Paralyze, Fear, All binds
Immune Stun, Death, Petrify, Panic, Curse
This box: view  talk  edit

The Yggdrasil Core is the final boss of Etrian Odyssey Untold. It is the main antagonist and final boss of Story mode, and the Classic mode superboss. In the main story, the player warps near its lair straight from B25F. The version fought as the final boss in the Story Mode is way weaker than the original core, due to a powerful composite used by the party to weaken it. In order to fight the Core at its full strength, you need to venture through to B30F of the Claret Hollows the long way after finishing the game. In Story Mode, the party can rematch the full-power Yggdrasil Core as many times as they want, while in Classic Mode the Yggdrasil Core respawns every 14 days like other on-field bosses.

When the party finally reaches the creature's lair, using the final geomagnetic pole, the Highlander uses the Yggdra Virus, given to them by Visil, on Yggdrasil Core, in order to greatly weaken it. Eventually, they manage to defeat it. Not long after that, however, the monster rises again, with its full power back. Kupala comes to the scene, revealing that her folk's original purpose was to help in destroying the core, and sacrifices herself, giving the Highlander's spear tremendous power; enough to defeat the beast. After a fierce battle, the party succeeds in defeating the mighty creature, bringing an end to its terror.


The following applies to the postgame Yggdrasil Core. The Story Mode finale Yggdrasil Core should be weak enough for the party to power through it without paying much attention to its patterns.

Like before, the Yggdrasil Core has an attack pattern. However, this time the boss will change between phases, each one with a distinct order of attacks. Each phase ends when enough damage is dealt, and is hinted by the use of Segment. The Yggdrasil Core will always open the fight with Necrosis. The first phase is mostly composed of Physical attacks with elemental attacks every five turns, following the order of Fire, Ice and Volt. When it enters the second phase, it will cast Activate, telegraphing status effects in the following turns, with an eventual physical attack and Cell Membrane. Phase 3 is a bit more random. While it focuses on elemental attacks every turn, following the aforementioned order, on every turn it has a chance of using a physical attack instead of one of its spells. Phase 4 is when it goes all-out, where its chosen attacks become more random.

Keep in mind that, while the Core's resistances are extremely high, it can be bound. A character with high amounts of luck and tec is recommended if you're using those. Challenging the Core on Expert may mandate the use of several King Grimoires due to the incredible utility they offer both offensively and defensively, particularly Yggdrasil Vaccine for Ancient Pollen.

While most of the boss' attacks are extremely dangerous, two of them are noteworthy: Root Cyclone and Armageddon. Both attacks inflict extreme amounts of damage, and on higher difficulties may require use of skills such as CPR to survive. Root Cyclone can be blocked with Parry and other similar skills. Armageddon, however, happens outside its attack pattern. Whenever your party has 4 or more buffs at the end of a turn, an invisible countdown starts. This countdown can last as long as 16 turns at 4 buffs or as short as 8 turns at 12 to 15 buffs. The countdown pauses whenever the party falls to 3 or fewer active buffs, but will not reset. Once this countdown hits 0, the Core breaks the pattern to cast King's Resolve to erase the party's buffs, followed by the devastating Armageddon in the next turn. Armageddon deals so much damage that CPR or Offering Robe is mandated to survive it.

The details of each phase are detailed below:

Be aware that this data was taken from multiple fights with Yggdrasil's Core and may not entirely be accurate.

Phase 1: 90000 HP - 72900 HPEdit

  1. Necrosis
  2. Explode/Freezing/Thunderstorm
  3. Land Slash/Demonic Rush
  4. Demonic Rush/Land Slash
  5. Root Cyclone
  6. Return to step 2.

Of the elemental attacks, it always uses Explode first, and transitions to the next elemental attack when it repeats the loop. The physical attack of choice on step 3 is determined randomly, with the other unused attack selected on the next turn.

Phase 2: 72900 HP - 54900 HPEdit

  1. Segment (9999)
  2. Activate
  3. Entangling Ray/Necrosis/Ancient Pollen
  4. Land Slash/Demonic Rush
  5. Cell Membrane
  6. Ancient Pollen/Entangling Ray/Necrosis
  7. Explode/Freezing/Thunderstorm
  8. Return to step 2.

For steps 3, 6 and 7, it will use the first listed move, before using the next listed one whenever it repeats the loop.

Phase 3: 54900 HP - 36900 HPEdit

The Core takes a turn to heal 9999 HP via Segment like it did at the start of its previous phase. From this point, it chooses between two possible attack pattern:

Pattern A Pattern B
  1. Explode/Freezing/Thunderstorm
  2. Freezing/Thunderstorm/Explode
  3. Land Slash/Demonic Rush
  4. Root Cyclone
  5. Return to step 1 of either pattern.
  1. Explode/Freezing/Thunderstorm
  2. Land Slash/Demonic Rush
  3. Thunderstorm/Explode/Freezing
  4. Root Cyclone
  5. Return to step 1 of either pattern.

Regardless of which pattern it chose first, it will select Explode on step 1, and every subsequent instance of an elemental attack will depend on what element it chose previously. It always proceeds in the sequence of Fire-Ice-Volt.

Phase 4: 36900 HP - 0 HPEdit

This time, the Core takes a turn to restore 24000 HP via Segment. It will not heal for the rest of this battle. Just like the previous phase, it randomly chooses between two possible attack patterns:

Pattern C Pattern D
  1. Entangling Ray/Necrosis/Ancient Pollen
  2. Land Slash/Demonic Rush
  3. Explode/Thunderstorm/Freezing
  4. Thunderstorm/Freezing/Explode
  5. Root Cyclone
  6. Cell Membrane/Activate
  7. Return to step 1 of either pattern.
  1. Entangling Ray/Necrosis/Ancient Pollen
  2. Land Slash/Demonic Rush
  3. Explode/Thunderstorm/Freezing
  4. Root Cyclone
  5. Freezing/Explode/Thunderstorm
  6. Cell Membrane/Activate
  7. Return to step 1 of either pattern.

Its chosen attack on steps 1, 2 and 6 of either pattern is random. The first time it enters step 3, the elemental move it uses is random, and subsequent instances of step 3 will rotate elements in the Fire-Volt-Ice order. What elements it has used in steps 4 and 5 are dependent on the element it used in step 3.

Skills Edit

  • Explode (Uses Head): Powerful ranged fire attack to the whole party.
  • Freezing (Uses Head): Powerful ranged ice attack to the whole party.
  • Thunderstorm (Uses Head): Powerful ranged volt attack to the whole party.
  • Demonic Rush (Uses Arms): 3-6 strong melee stab attacks across random targets.
  • Land Slash (Uses Arms): 4 strong cut attacks to a single target.
  • Root Cyclone (Uses Legs): Powerful ranged bash damage to the whole party.
  • Activate (Uses Head): Increases ailment chance for 5 turns.
  • Necrosis (Uses Head): May instantly kill the whole party.
  • Ancient Pollen (Uses Head): May inflict random ailments on the whole party.
  • Entangling Ray (Uses Legs): May inflict random binds on the whole party.
  • Cell Membrane (Uses Arms): Blocks all attacks on this turn and launches a powerful counter-attack against the whole party for every attack used against it.
  • King's Resolve (Uses Head): Removes all of the party buffs. Used at random points of the fight if your party has a large amount of buffs. The boss will always use Armageddon on the next turn.
  • Armageddon (Uses Head): Incredibly powerful ranged untyped attack to the whole party. Nearly impossible to survive via normal means, as it easily inflicts over 2000 damage.
  • Segment (Uses ???): Recovers a massive amount of health and moves into the next attack phase.

Drops Edit

  • Demon Core (Worth: 35000 en)
  • None.
  • True Demon Core (Worth: 1000000 en)

Conditional Drop Edit

  • The Yggdrasil Core's conditional drop has a unique condition. In order to get the True Demon Core, you must defeat the boss in its full power. That means that fighting it at the end of the story mode will not count, as the Yggdrasil Core is weakened during that fight. In order to obtain the item in the story mode, you must fight the boss again on the post-game, at the end of the Claret Hollows. This is not a problem in the Classic Mode, as the boss can only be fought at its full strength. However, if you played only Classic Mode, you cannot get the Demon Core which is used to make the Ameno-Habakiri, the strongest katana in the game. Keep in mind that using a formaldehyde during the story mode fight will NOT drop the item, even though both fights share the same codex entry. The True Demon Core does not unlock anything in the shop, and just sells for 1,000,000 en.


  • Although Primevil has no back-story in Etrian Odyssey, it was given one which its remake, Etrian Odyssey Untold's plot, revolved around. If you compare Yggdrasil Core's (Primevil renamed in the remake) back-story with Etrian Odyssey IV's final boss, the Heavenbringer, both histories are in a way very similar. This fact gives a possible hint that both EO1/EOU and EO4 takes place in the same universe, which is later confirmed in Etrian Odyssey 2 Untold, which establishes that all games take place in the same world.
  • Primevil's battle theme in Untold, With Much At Stake, is a remix of a song called The Battlefield that Never Sleeps, found in the first Etrian Odyssey's soundtrack, but was never used for unknown reasons. The FM version of the song is the same as the original.