Zenothlee

Zenothlee is an Elemental Beast created by Evol. It is found in the Cold Lab in the Darkness Ruins. Fought once during the main storyline, it is replaced by the optional Serpent boss during Chapter Three. However, once the first ending is completed, Zenothlee respawns in the Cold Lab as a Level 200 superboss and the strongest enemy in the game.

Story
One of the Elemental Beasts created in pursuit of Quanlee, Zenothlee is considered a "failed experiment" by Evol. Like the other Elemental Beasts it was created using elemental energy in the Spiritual Atrium, however unlike its predecessors, all discovered as corpses, it is actually alive.

After Evann and Lutina return from examining the mural at the army base in Escarre, the party realises Evol is deeper down Starry Corridor than they initially believed. Heading further down, they explore the Darkness Ruins, where Kroitz and his men have already found Evol's research facility and the Elemental Beast guarding it.

Upon entering the Cold Lab, Evann finds a lone soldier laying injured on the floor. Succumbing to his wounds, the soldier speaks vaguely of something that was overwhelming and "too much for them to handle". Lacking clarity, he seems to mistake Evann for Kroitz, calling him "Colonel" and apologising for having "abandoned everyone". Evann tells him to hang on and that he'll help him, but it seems too late.

Appearing at the window ledge above the Cold Lab's door, which he locks remotely, trapping everyone inside, Kroitz announces that he has obtained all the information he needs about Evol, and that he'll leave the "failed experiment" to deal wtih Evann and his party. Zenothlee then appears at the far side of the room, pursuing the overwhelmed soldiers who are fleeing from it. Evann must defeat it to go further into Evol's research facility and find a way to unlock the door.

Battle Strategy
Not only does Zenothlee have exceptional ACT, it is accompanied by several Crystals that cannot be destroyed completely, making the battle a challenge from the start. It is possible to deplete the HP of a Crystal, however after a certain amount of time it will reactivate. It is best to ignore the Crystals unless cancelling their moves, but if their HP is fully depleted they do offer Skill Points.

Speedy is useful here for keeping the party on a similar level of ACT as Zenothlee. Diggin can also be helpful for defending against its Titan Cannon move, which hits the whole party multiple times and can rack up some damage if you're not careful. Zenothlee also has a Feat it can pull of with an individual Crystal called Crystal Capture, which will pin a character down and stop their movements entirely. A turn must be spent attacking said Crystal in order to free the character.

Zenothlee can be affected by Poison, which can help chip away at its HP whilst the characters focus on cancelling upcoming moves. The Crystals have a powerful Crackle Floe spell which, whilst a single-target spell, can be devastating if two or more of them gang up on a single character with it.