Sea of Stars Forbidden Cavern Walkthrough and Boss Slug Guide

To clear the Forbidden Cavern in Sea of Stars, lower the blue energy barrier using the floor switch on the west path, retrieve the Forbidden Cavern Key from the eastern ledges, unlock the central gate, and defeat the Boss Slug by breaking its damage locks.

Party Preparation and Combat Roles

Before entering the cavern, verify your equipment and party resources at the campfire outside the entrance. Log your save at the open-air book pedestal and confirm all party members are at full HP and MP.

Garl’s Nourish skill restores HP using an apple without consuming finite inventory items. Rely on this skill to preserve recovery items for emergencies. During battles with basic cave enemies such as bats and shelled bugs, defeat them to generate Live Mana on the ground. You can leave this unabsorbed during easier skirmishes to keep party resources steady.

Exploring the Cavern and Finding the Key

The main entrance foyer contains a locked central iron gate flanked by dual pedestals. You must navigate the side paths to find the key and open the way forward.

1. Lower the Blue Barrier: Head through the open doorway to the left (west). Climb the textured ivy along the rock walls and leap across the stone pillars toward the north wall to reach a floor button. Step on this switch to disable the blue barrier and open the upper catwalk.
2. Collect the Adventurer's Vest: Along the upper western ridge, climb down an ivy ladder into a lower nook. Open the chest to obtain the Adventurer’s Vest, then open your equipment menu to equip it on Zale or Valere for extra physical defense.
3. Drop the Shortcut Ladder: Proceed along the raised northern ledge to find a tied rope ladder. Interact with it to kick it down to the campfire level, establishing a direct shortcut back to the entrance save point.
4. Retrieve the Forbidden Cavern Key: Enter the eastern archway. Jump across the floating stone platforms across the gaps to reach an ornate chest resting on an elevated dais. Open it to acquire the Forbidden Cavern Key.
5. Unlock the Inner Sanctum: Return through the central foyer via your shortcut ladder. Interact with the lock mechanism on the central iron door to insert the key and access the boss arena.

How to Beat the Boss Slug

The Boss Slug remains stationary in the back row while regularly summoning smaller slug minions into the front row.

• Clear Minions Efficiently: The slug adds deal steady chip damage if left active. Cast Valere’s Crescent Slash to damage multiple front-row targets at once. Use standard physical attacks from Garl or Zale to finish off damaged minions while restoring MP.
• Break Charged Attack Locks: When the Boss Slug prepares its heavy sludge spit attack, lock icons appear above its head. Use Zale’s sword strikes or Sunball to break slashing and solar locks, and use Valere’s staff attacks to clear blunt locks.
• Mitigate Incomplete Locks: If you cannot clear every lock before the countdown timer hits zero, break as many individual icons as possible. Each broken lock directly reduces the total damage of the incoming attack.
• Maintain Party Health: Direct Garl to cast Nourish on any party member whose health falls below half, allowing Zale and Valere to prioritize lock breaking.

Next Step: The Mountain Trail

Once the Boss Slug is defeated, it dissolves and opens the rear passage of the cavern. Head through the archway to exit into the daylight on the Mountain Trail.

Stop at the cliffside rest area to set up camp before proceeding up the mountain toward the Elder Mist. Speak with Garl at camp to prepare Berry Jam using the ingredients collected inside the cavern. Keeping a full stock of healing meals ensures you can restore health during upcoming platforming sections and mountain encounters without draining combat MP.