Here I'm going to cover both versions of the Yggdrasil Core that you can fight in Untold. There's the one that serves as Story mode's final boss, and the one you can fight at the end of the post-game. This is one of the few times in the series where the Monstrous Codex outright lies to you, as the version you fight in Story mode and the one you fight in the post-game are two entirely separate enemies with different stats and whatnot, and only the post-game Yggdrasil Core's stats will be shown in the codex. Not only that, it claims that the Demon Core is the Yggdrasil Core's normal drop, while the True Demon Core is its conditional drop. In reality, since they are two separate enemies, each version of the Yggdrasil Core can only drop one item. Meaning that using a Formaldehyde in either of these fights will not get you both drops.

Let's look at the one that the Story party fights first.

Yggdrasil Core

Level: 64

HP: 90000

STR: 66

VIT: 53

AGI: 42

LUC: 55

TEC: 55

Exp: 1000000

Attack Type: Bash

Drop 1: Demon Core - 100% Drop Rate.

Drop 2: N/A

Drop 3: N/A

Damage Resistances:

Cut: 150%

Bash: 150%

Stab: 150%

Fire: 200%

Ice: 200%

Volt: 200%

Almighty: 150%

Ailment Resistances:

Sleep: 50%

Panic: 20%

Poison: 100%

Blind: 30%

Curse: 50%

Paralysis: 30%

Terror: 30%

Bind Resistances:

Head: 30%

Arm: 50%

Leg: 75%

Other Resistances:

Death: 0%

Petrification: 0%

Stun: 10%

Skills:

Land Slash (Grimoire Skill): Uses the Arms. A STR based melee Cut attack that attacks one person 4 times. Deals 45% damage per hit. 80% speed. 85 hit rate.

Demonic Rush: Uses the Arms. A STR based melee Stab attack that randomly attacks everyone 3 to 6 times. Deals 55% damage per hit. 70% speed. 85 hit rate.

Activate (Grimoire Skill): Uses the Head. Places a buff on the user that increases the success rate of skills that inflict Instant Death, ailments, and binds by 300% for 6 turns. 70% speed.

Necrosis: Uses the Head. Attempts to inflict Instant Death on the entire party. Has a 10% success rate. 60% speed.

Armageddon (Grimoire Skill): Does not use a body part. A TEC based ranged Almighty attack that deals 180% damage to the entire party. 30% speed. 150 hit rate.

Cell Membrane: Uses the Arms. Blocks all incoming damage for the current turn. For every attack that was blocked, the Yggdrasil core will counterattack with a combination of Cut, Stab, Bash, Fire, Ice, Volt, Almighty, or Untyped damage, depending upon which attacks were used against it. The counterattacks deal 100% of the damage it was supposed to take. Has priority, so it will always go first. 99 hit rate.

Segment: Does not use a body part. Restores 2400, 4800, 9999, 12399, or 14799 HP when used. 500% speed. Used to signal the beginning of a phase. The amount healed is dependent upon which phase is reached, and how many phases were skipped to reach it.

Explode: Does not use a body part. A TEC based ranged Fire attack that deals 170% damage to the entire party. 60% speed. 120 hit rate.

Freezing: Does not use a body part. A TEC based ranged Ice attack that deals 170% damage to the entire party. 60% speed. 120 hit rate.

Thunderstorm: Does not use a body part. A TEC based ranged Volt attack that deals 170% damage to the entire party. 60% speed. 120 hit rate.

Tangling Ray: Uses the Legs. Attempts to inflict head binds, arm binds, and leg binds on the entire party. Has a 20% success rate. 70% speed.

King's Resolve: Uses the Head. Erases all buffs that are on the party. 120% speed.

Root Cyclone: Uses the Legs. A STR based ranged Bash attack that deals 100% damage to the entire party. 30% speed. 99 hit rate.

Ancient Pollen: Uses the Head. Attempts to inflict Petrification, Sleep, Blind, Curse, and Paralysis on the party. Has a 7% success rate. 30% Speed.

The Yggdrasil Core has 2 phases. During phase one, the Highlander will use the virus against the Yggdrasil Core (coded as an Untyped attack called Yggdra Virus) that deals 75000 damage to it, leaving only 15000 HP left. Unfortunately, due to an oversight, the attack was coded as a melee attack, meaning that if the Highlander is in the back row at the start of the battle, and does not have a ranged weapon equipped, Yggdra Virus only deals 37500 damage instead, and the Yggdrasil Core will be left with 52500 HP. At any rate, the first phase follows this attack pattern:

Turn 1: Attack.

Turn 2: Explode, Freezing, or Thunderstorm. It will use Explode on the first loop, Freezing on the 2nd loop, Thunderstorm on the 3rd loop, and so on.

Turn 3: Land Slash or Demonic Rush.

Turn 4: Land Slash or Demonic Rush. Yggdrasil Core will not use the skill it used on turn 3.

Turn 5: Root Cyclone.

And then loops from turn 1.

After killing the Yggdrasil Core once, it will enter phase 2. This time, you must deplete all of its HP and not just a small portion. The Story mode party gets a power boost that triples their damage output against the Yggdrasil Core during this phase. The pattern phase 2 follows is exactly the same as the pattern the Yggdrasil Core you fight in the post-game follows, which I will cover below.

Yggdrasil Core

Level: 99

HP: 90000

STR: 99

VIT: 75

AGI: 65

LUC: 85

TEC: 99

Exp: 1000000

Attack Type: Bash

Drop 1: N/A

Drop 2: N/A

Drop 3: True Demon Core - 100% Drop Rate.

Damage Resistances:

Cut: 100%

Bash: 100%

Stab: 100%

Fire: 125%

Ice: 125%

Volt: 125%

Ailment Resistances:

Sleep: 20%

Panic: 0%

Poison: 50%

Blind: 20%

Curse: 0%

Paralysis: 10%

Terror: 10%

Bind Resistances:

Head: 20%

Arm: 20%

Leg: 30%

Other Resistances:

Death: 0%

Petrification: 0%

Stun: 0%

Skills:

Land Slash (Grimoire Skill): Uses the Arms. A STR based melee Cut attack that attacks a single target 4 times. Deals 115% damage per hit. 150% speed. 95 hit rate.

Demonic Rush: Uses the Arms. A STR based melee Stab attack that randomly attacks everyone 3 to 6 times. Deals 135% damage per hit. 80% speed. 95 hit rate.

Activate (Grimoire Skill): Uses the Head. Places a buff on the user that increases the success rate of skills that inflict Instant Death, ailments, and binds by 500% for 6 turns. 70% speed.

Necrosis: Uses the Head. Attempts to inflict Instant Death on the entire party. Has a 15% success rate. 70% speed.

Armageddon (Grimoire Skill): Does not use a body part. A TEC based ranged Almighty attack that deals 800% damage to the entire party. 30% speed. 200 hit rate.

Cell Membrane: Uses the Arms. Blocks all incoming damage for the current turn. For every attack that was blocked, the Yggdrasil core will counterattack with a combination of Cut, Stab, Bash, Fire, Ice, Volt, Almighty, or Untyped damage, depending upon which attacks were used against it. The counterattacks deal 250% of the damage it was supposed to take. Has priority, so it will always go first. 99 hit rate.

Segment: Does not use a body part. Restores 9999, 19998, 24000, 33999, or 43998 HP when used. 500% speed. Used to signal the beginning of a phase. The amount healed is dependent upon which phase is reached, and how many phases were skipped to reach it.

Explode: Does not use a body part. A TEC based ranged Fire attack that deals 450% damage to the entire party. 100% speed. 200 hit rate.

Freezing: Does not use a body part. A TEC based ranged Ice attack that deals 450% damage to the entire party. 100% speed. 200 hit rate.

Thunderstorm: Does not use a body part. A TEC based ranged Volt attack that deals 450% damage to the entire party. 100% speed. 200 hit rate.

Tangling Ray: Uses the Legs. Attempts to inflict head binds, arm binds, and leg binds on the entire party. Has a 20% success rate. 70% speed.

King's Resolve: Uses the Head. Erases all buffs that are on the party. 120% speed.

Root Cyclone: Uses the Legs. A STR based ranged Bash attack that deals 420% damage to the entire party. 50% speed. 110 hit rate.

Ancient Pollen: Uses the Head. Attempts to inflict Petrification, Sleep, Blind, Curse, and Paralysis on the entire party. Has a 10% success rate. 80% Speed.

This is the true Yggdrasil Core, which is significantly stronger than its Story mode counterpart. Not only are its stats much higher, its attacks are far more powerful as well. Now let's look at its attack pattern.

Phase 1: 90000 to 72900 HP

Turn 1: Necrosis.

Turn 2: Explode, Freezing, or Thunderstorm. It will use Explode on the first loop, Freezing on the 2nd loop, Thunderstorm on the 3rd loop, and so on.

Turn 3: Land Slash or Demonic Rush.

Turn 4: Land Slash or Demonic Rush. Yggdrasil Core will not use the skill it used on turn 3.

Turn 5: Root Cyclone.

And then it loops from turn 2.

Phase 2: 72900 to 54900 HP

Turn 1: Segment.

Turn 2: Activate.

Turn 3: Tangling Ray, Necrosis, or Ancient Pollen. It will use Tangling Ray on the first loop, Necrosis on the 2nd loop, Ancient Pollen on the 3rd loop, and so on.

Turn 4: Land Slash or Demonic Rush.

Turn 5: Cell Membrane.

Turn 6: Ancient Pollen, Tangling Ray, or Necrosis. It will use Ancient Pollen on the first loop, Tangling Ray on the 2nd loop, Necrosis on the 3rd loop, and so on.

Turn 7: Explode, Freezing, or Thunderstorm. It will use Explode on the first loop, Freezing on the 2nd loop, Thunderstorm on the 3rd loop, and so on.

And then it loops from turn 2.

Phase 3: 54900 to 36900 HP

Turn 1: Segment.

Turn 2: Explode, Freezing, or Thunderstorm. It will use Explode on the first loop, Freezing on the 2nd loop, Thunderstorm on the 3rd loop, and so on.

In this phase, Yggdrasil Core has 2 different patterns it can follow on a given loop. After turn 2, it will choose one of the following patterns randomly.

Pattern A:

Turn 3: Explode, Freezing, or Thunderstorm. The attack used here is dependent upon the attack used on turn 2. It will use Freezing if Explode was used, Thunderstorm if Freezing was used, or Explode if Thunderstorm was used.

Turn 4: Land Slash or Demonic Rush.

Turn 5: Root Cyclone.

And then it loops from turn 2.

Pattern B:

Turn 3: Land Slash or Demonic Rush.

Turn 4: Explode, Freezing, or Thunderstorm. The attack used here is dependent upon the attack used on turn 2. It will use Thunderstorm if Explode was used, Explode if Freezing was used, or Freezing if Thunderstorm was used.

Turn 5: Root Cyclone.

And then it loops from turn 2.

Phase 4: Until death

Turn 1: Segment.

Turn 2: Tangling Ray, Necrosis, or Ancient Pollen.

Turn 3: Land Slash or Demonic Rush.

Turn 4: Explode, Freezing, or Thunderstorm. The skill it uses on the first loop is entirely random. The attack it uses on the next loop depends on which attack was used in the first loop. It will use Freezing if Explode was used, Thunderstorm if Freezing was used, or Explode if Thunderstorm was used. Yggdrasil Core will continue to follow this pattern on further loops.

In this phase, Yggdrasil Core has 2 different patterns it can follow on a given loop. After turn 4, it will choose one of the following patterns randomly.

Pattern C:

Turn 5: Explode, Freezing, or Thunderstorm. The attack used here is dependent upon the attack used on turn 2. It will use Thunderstorm if Explode was used, Explode if Freezing was used, or Freezing if Thunderstorm was used.

Turn 6: Root Cyclone.

Turn 7: Cell Membrane or Activate.

Pattern D:

Turn 5: Root Cyclone.

Turn 6: Explode, Freezing, or Thunderstorm. The attack used here is dependent upon the attack used on turn 2. It will use Freezing if Explode was used, Thunderstorm if Freezing was used, or Explode if Thunderstorm was used.

Turn 7: Cell Membrane or Activate.

And then it loops from turn 2.

When Yggdrasil Core uses Segment at the start of phases 2 and 3, it will heal itself for 9999 HP (2400 in Story mode.) The Segment used at the start of phase 4 heals the Yggdrasil Core for 24000 HP (9999 in Story mode.) However, if you skip any phases, the amount healed from Segment will increase depending on how many phases you've skipped. So if you skipped straight to the last phase from the start of the battle, the Yggdrasil Core will heal itself for 43998 HP. (9999 + 9999 + 24000 = 43998.) In Story, that would be 14799 HP. (2400 + 2400 + 9999 = 14799.)