Thessal the Mermaid Goddess

Last updated: Exalt Version (Mar 2023)

Thessal the Mermaid Goddess is the boss of the Ocean Trench.

The Realm Eye says:
Thessal is the ruler of the realm beneath the waves, but her kind had struggled to survive since mortals became capable of naval combat.
Her contact with the surface world is limited, but when Oryx came to her with a treaty for mutual protection, she agreed out of desperation.
With Thessal’s dominion over sea monsters and Oryx’s strengthening magic, the duo created the Hermit God to stop ships from ever setting sail again.



Base HP: 51,750 (Boss Adaptive Scaling Boss Adaptive HP Scaling)
DEF: 60
EXP: 30,000
Location: Ocean Trench

Quest Monster
Immune to Stasis
Immune to Paralyzed
Immune to Stun
Counts towards Humanoid Kills
Counts towards God Kills

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Aesthetics Damage Condition effects Speed (tiles/sec) Range (tiles) Comments
Thunder Swirl 100 Gold Four Pointed Star Armor Broken for 4s 5.5 8.8 Piercing Shots hit multiple targets
Trident 65 7 21 Piercing Shots hit multiple targets
Super Trident 100 6 18 Piercing Shots hit multiple targets
Yellow Wall 120 Weak Icon Weak for 6s 6 18 Piercing Shots hit multiple targets


Thessal is found in a large square room at the end of the Ocean Trench, with each side having a small alcove with an air vent for players to restore oxygen with. Upon being approached, she will immediately attack.

Phase 1

Thessal wanders in the middle of the room, cycling between two attacks:

  • Rapidly firing 4-way pairs of gold Super Tridents nine times, alternating between firing them along the cardinal and diagonal directions. Right before using this attack, Thessal will go invulnerable for 1.6 seconds.
  • Flashing pink and firing four rings of 8 gold Thunder Swirls that inflict Gold Four Pointed Star Armor Broken. Thessal gains immunity to Gold Five Pointed Star Stunned during this attack.

During all attacks, she will also continuously throw Coral Bombs, either directly at players or in random spots in the boss room. These will explode into a ring of pink Pet Stasis Pet Stasis shots and each split into six smaller Coral Bombs that do the same, quickly causing large storms of bullets.

In addition, she constantly keeps a Deep Sea Beast on each of the 4 air vents in the room, making it much harder to regain air. If one dies, she will respawn it after a short delay.

Phase 2

At 50% HP, Thessal flashes yellow, moves to the center of the room, and fires three dense rings of shockwaves that inflict Weak Icon Weak, also gaining Stun Immunity for this attack. After using it for the first time, she will use this attack again after every Thunder Swirl attack. Her prior attacks will also be improved:

  • Her Super Trident attack now fires 11 times with increased frequency
  • Her Thunder Swirl attack now fires 16 shots per ring.
  • The frequency and number of Coral Bombs she spawns will be increased.

Phase 3

At 20% HP, Thessal will immediately use her shockwave attack again, but will also go invulnerable for 8 seconds upon hitting the HP threshold.

  • Her Super Trident attack will now fire 13 times in succession with the delay between cardinal/diagonal bursts significantly reducing (giving the impression of her simultaneously firing diagonally and cardinally). This does not include the first burst, which will be normal.
  • Her Thunder Swirl attack now fires 5 times in succession with slightly less delay between rings.
  • The frequency/number of her Coral Bombs will go up again.
Dying Thessal He lives and reigns and conquers the world

Occasionally, either by pure luck or if the dungeon has the “Alexander’s Legacy I/II” modifier,, when Thessal is killed, instead of dying, she will crumple over the loot bag and ask, “Is King Alexander alive?” If you respond with “He lives and reigns and conquers the world”, she will say “Thank you, kind sailor.” and spawn 3 Coral Gifts before vanishing.

If nobody says the right answer after a few seconds, she’ll shout “You speak LIES!”, suddenly rising up, going invulnerable, and launching a relentless attack consisting of all her attacks simultaneously fired at a nonstop pace. After roughly ten seconds of attacking, Thessal will self-destruct (although her original loot will still have already been dropped).

If you are standing on her when this happens (not smart), this will be instant death. Period.


Deep Sea BeastDeep Sea Beast
Coral Bomb BigCoral Bomb Big
Coral GiftCoral Gift

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Tips and Strategies

In general, avoid her Armor Breaking shots at all costs. A run-in with a Coral Bomb, Deep Sea Beast, or Thessal herself with 0 DEF can easily be lethal.

For her trident attack, standing directly left/right/above/below her or directly diagonally from her will let you slip between the trident pairs if you aren’t too close. Note that Thessal moves slightly when attacking, so that needs to be taken into account. For her wave attack, you can duck between the individual waves if you stand far back enough, or you can use the four pillars in her arena as cover.

If you have a small group/soloing or if you expect the fight to last a long time, it can be helpful to clear the room right before her chamber so that you have access to an air vent that is not guarded by monsters. This also prevents unwanted confuse or paralyze enemies from joining the fight.

When in combat, do not hug Thessal, because she will sometimes move forwards very fast and instantly let loose a huge circle of shots. If you are hugging her, you won’t have time to back away, and her shots will do massive damage, which could lead to an insta-kill.

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In Release X.12, the Thessal fight received a significant buff because it was considered to be extremely easy with even a small group of players, to the point of Thessal dying in seconds with a medium-large group. The following changes were made:

  • Paralyze immune
  • HP increased from 69,000 to 96,000
  • Coral Bombs inflict Pet Stasis for 8 seconds
  • Yellow Wall inflicts Weak for 6 seconds
  • Increased Thunder Swirl Armor Break duration from 2.4s to 4.0s
  • Can’t be stunned during Armor Break and Yellow Wall phases (warns with purple flash at the end of Tridents)
  • Small invulnerability during Tridents (2.6s) and at the start of the last phase (8s)
  • Shoots Tridents faster in the first phase, Armor Break slightly faster in the first and second phase
  • All shots (including Coral Bombs’) now pass through players
  • Deep Sea Beasts inflict Slowed for 2 seconds

In Patch X.26.0.0 (May 2018), additional changes were made, which include reverting Thessal’s base HP back to 69,000 but giving her HP scaling this time, alongside the Coral Gifts which received a significant HP boost and HP scaling as well.

In Exalt Version (July 2020), additional changes were made, which including reducing Thessal’s HP by 1/4 but giving her Adaptive HP scaling.

The Arctic Bow has previously dropped from Thessal (winter 2016-17 only).

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Thessal is based on a Greek legend called “The Legend of Thessalonike”. In the legend, Thessalonike was the sister of King Alexander the Great. When the king died, Thessalonike tried to kill herself by jumping into the sea, but became a mermaid instead of dying. She then asked sailors who encountered her: “Is Alexander the King alive?” She would only let them pass if they answered: “He lives and reigns and conquers the world.” Any other answer would cause her to fly into a rage and destroy the ship and its crew.

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