Zy'tl Q'ae (ザイトルクワエ) was a massive tree monster that dwelled in the Great Forest of Tob.
Zy'tl Q'ae was described to be a monster that easily dwarfs the 4th Floor Guardian of Nazarick, Gargantua. It is a giant tree that stands almost 100 meters in height, with six branching tentacles that extend to the length of over 300 meters. Decorating the top of its head, a patch of green-like moss grows. And in the middle of its great trunk lies a gaping cavernous maw with sharp teeth.
Very little is shown about the personality of Zy'tl Q'ae if any. Its actions suggest it to be akin to a mindless beast with a voracious appetite whose only goal is to devour all things. It is possible that Zy'tl Q'ae was once intelligent when it was a treant, but it seems that its current state has made it lose all ability to be reasoned with.
Long ago in the distant past, this evil tree known as Zy'tl Q'ae was originally a treant that Pinison described as 'twisted'. According to her, the evil tree was one of the many monsters that appeared in the New World, falling from a tear in the sky. These creatures it came with were incredibly powerful, rumored to have the power to destroy the world and said to rival a Dragon Lord.
While many of the monsters were eliminated or sealed over the ages, a few like the evil tree survived and went into hiding. Taking residence in the northern part of the Great Forest of Tob, it fell into a deep slumber. On occasion, it would feed to replenish its strength by draining the life force of the surrounding plants and trees.
During one of its many partial awakenings, a party of seven adventurers passed through the Forest of Tob and challenged the great monster so as to restore peace in the forest at the behest of a dryad. The tree was then given the name Zy'tl Q'ae by the leader of the group. The seven managed to defeat the monster. However, they only defeated a piece of its body. The main body had not fully awakened and would not do so until a long, but indeterminate, the time had passed.
The Sealed Evil Tree Arc
- Main article: The Sealed Evil Tree Arc
Zy'tl Q'ae reveals itself before Ainz and Aura who are led to its home by Pinison. Upon awakening, it immediately starts to use its tentacles limbs, ripping great trees from their roots and devouring them. While the treant goes about feasting, it takes notice of the intruders in its domain. The Floor Guardians then arrive at Ainz's command. Finding the constant roar annoying as they are holding a conversation about what to do with Zy'tl Q'ae, Demiurge uses magic to freeze the great tree in ice. Though incapacitated, Zy'tl Q'ae manages to break free from its entrapment, more furious than ever. Turning its sole attention to the Guardians, the treant attempts to crush them with its tree limbs.
The Floor Guardians carefully fend off the treant's attacks through a combination of their strength and teamwork. Eventually, Ainz Ooal Gown steps in, satisfied with their coordination; he freezes Zy'tl Q'ae in time, decorating its trunk with numerous vessels of exploding spheres, making the fearsome treant look like a Christmas tree, before exploding.
The Two Leaders Arc
- Main article: The Two Leaders Arc
Aura reported to Ainz that after she and her fellow Floor Guardians fought that tree monster called Zy’tl Q’ae, she did a quick sweep of the Great Forest of Tob, aside from the underground caverns, which she didn’t investigate. In the end, Aura stated that she didn’t find any strong enemies like the tree monster.
Abilities and Powers 
Zy'tl Q'ae was the first impressive creature that Ainz had encountered in the New World. Aura estimated its power level to be ranging between level 80 to 85. Unfortunately, Aura was unable to exactly measure its HP which she declared to be 'off the chart'.
Pinison once declared that its strength rivaled a Dragon Lord, possibly the ones from the Eight Greed Kings' era. Specializing in using its great size and strength to its advantage, it is able to uproot trees and objects from the surrounding area, lifting them with ease.
Also, Zy'tl Q'ae possessed great endurance, as it was able to shake off Demiurge's Frost of Judecca after some time. Meanwhile, it could recover from multiple attacks by the combined might of the Floor Guardians, despite the attacks were not aimed to kill. In addition to all that, Zy'tl Q'ae can produce seeds and shoot them as projectiles.
However, despite the monster's "off the chart" health, the Floor Guardians deemed it to be weak and it would have been easily defeated by only one Guardian should any of them wanted to do so.
- Zy'tl Q'ae could be one of the surviving Evil Deities that fought the Thirteen Heroes.
- Its name originated from an eldritch race of plant monsters from Cthulhu Mythology.
- Ironically, a rare healing herb grows at the top moss area of its head.
- Ainz mused that giant trees were a joke during the early days of YGGDRASIL.
- According to Ainz, there is a similar creature to Zy'tl Q'ae in YGGDRASIL, but it is unknown if Zy'tl Q'ae is native to the New World or a remnant from YGGDRASIL.
- According to Ryraryus Spenia Ai Indarun, the dark elves that used to be the lords of the forest of Tob were driven away because of the Evil Tree taking residence there.
- Interestingly, the second part of the Web Novel reveals the existence of the Demon Tree Dragon Lord which possessed similar traits to Zy'tl Q'ae.
- Zy'tl Q'ae is referred to as an Arbor Mala, this translates to "Bad Tree" in Latin.
- In Mass for the Dead, a tree monster with similar abilities to Zy'tl Q'ae was found by Nazarick during a quest to search for the Supreme Odor Flower. According to the rumors in E-Rantel the tree was encountered by a hero who vowed to kill it when it returned. After it was slain, the tree was found to be still germinating, and its tree rings indicated it was a thousand years old. Given that it's age, story and characteristics it may have been the Evil Tree, though it was left unnamed as Pinison was absent in the game story.