Slayers 2 Final Selection: How to Find and Defeat Lost

Lost is the underwater boss that gates the Submerged Key step of Final Selection in Slayers 2. The objective reads “Defeat Lost 0/2” and splits into two tasks: killing Lost and picking up the Submerged Key that spawns after the fight. Both happen inside a hidden cavern beneath a cliffside pond.

Quick answer: From Demon Trees, head to the cliff pond roughly 300 meters away, dive into The Forgotten Lake, swim through the submerged cave mouth, defeat Lost (Level 30, 790 HP), then press T on the glowing Submerged Key.

Lost boss stats and location

The full boss name is “The Lost Serpent Lost.” It waits in a dry chamber that you can only enter by swimming down through the pond. The entrance sits along a rocky wall underwater, so you will not see it from the surface.

Detail	Value
Boss	The Lost Serpent Lost
Level	30
Health	790 HP
Location	Cave under the cliff pond (The Forgotten Lake)
Distance from Demon Trees	Roughly 300 meters

How to reach the underwater cave

Begin at the Demon Trees safe area, then head toward the cliff overlook’s rim. Continue northwest until the water below the drop comes into view, roughly 300 meters away.

Navigating to the Pond — The cliffside path that leads down to the target pond near Demon Trees. Shown at 00:38 in Abooga1’s video. Image: Ouw Productions

Jump off the ledge and dive deep into the water. The location name changes to The Forgotten Lake and an air meter appears in the HUD. Keep descending while watching that oxygen bar.

Diving Underwater — Diving through The Forgotten Lake while the air gauge counts down. Shown at 00:50 in Abooga1’s video. Image: Ouw Productions

Swim through the opening beneath the water in the rock face. It rises into a dry cavern within, where surfacing lets your air refill.

Finding the Cave Entrance — Inside the dry cavern after passing through the underwater cave mouth. Shown at 01:02 in Abooga1’s video. Image: Ouw Productions

If your oxygen runs low before you find the gap, resurface, refill, and dive again close to the same spot rather than pushing through with an empty meter.

How to defeat Lost

Follow the dry path forward and Lost appears with an overhead nameplate and a full 790 HP bar. The fight is entirely melee, using sword and water techniques inside the tight cavern space.

Boss Overview — Lost at full health with its listed drops before the fight begins. Shown at 01:12 in Abooga1’s video. Image: Ouw Productions

Lost attacks with quick strings of multiple hits and moves that break your guard; trying to stand your ground and trade blows will quickly cost you health. Parry incoming strikes, evade the guard breaks, and conserve stamina between blocks.

Boss Battle — Blocking and countering Lost's combos while whittling down its health bar. Shown at 02:21 in Abooga1’s video. Image: Ouw Productions

Keep your spacing wide, punish the recovery after Lost finishes a combo string, and block or parry rather than tanking the multi-hits. Whittling the bar down to zero ends the encounter.

Lost drops and rewards

Defeating Lost pays out mastery and currency along with a chance at a rare schematic. The rewards land on the cavern floor as pickups next to the body.

Reward	Amount / Chance
Yen	+15
Water, Sword and Spear Mastery	+412
Metal Scraps	Guaranteed pickup
Shotgun Schematic	5% chance

Defeating Lost & Gathering Drops — Lost's body next to the Metal Scraps drop as the Yen and mastery rewards pop up. Shown at 03:15 in Abooga1’s video. Image: Ouw Productions

Collect the Submerged Key and confirm the objective

When Lost falls, a prompt gives the hint, “He’s dead! Then dive. The key waits below.” The Submerged Key appears on the cavern floor as a glowing white sphere. Approach it and press T to collect it.

You know the step is done when both parts of the tracker fill in: “Lost 1/1” for the kill and “Submerged Key 1/1” for the pickup. With the key in hand, swim back out of the cave and return to the Mizunoto to unlock the next stage of Final Selection.