Here's a comprehensive guide for the Mantis Secret Lair sidequest on Starfield. The Starfield Mantis sidequest rewards the Mantis legendary gearset and the Razorleaf starship, all for free.

Starfield Mantis Quest

You can do this quest at any point in the game, as long as you acquire the required tape to initiate it. It will put you through a drawn-out battle versus humans and machines alike, but the rewards you get at the end are absolutely worth it. It rewards you with an amazing ship and a legendary armor set for free, as long as you make it through the hordes of Spacers in the lair.

Starting the Quest

The first thing you'll need is the “Secret Outpost!” tape, which drops randomly from a Spacer. It's unremarkable and looks like any other note in the game, but keep an eye out as it contains crucial information on locating the Mantis lair.

In fact, you may already have this sitting in your inventory if you've been going around looting Spacers – simply interact with it upon finding it among your Notes to initiate the quest.

Arriving at Denebola I-b

Before you land on Denebola I-b, make sure you're prepared for an intense fight. Upon exiting your ship, you'll be attacked immediately, and there's no option for stealth. Equip your best gear and get ready for a tough battle. Having a companion also helps; I brought Sarah Morgan and she was more than happy to take down a lot of enemies for me.

Also note that you're also going to go against some Robots, apart from the high-leveled Spacers patrolling the area. Equip accordingly.

Livvey

In the middle of your Spacer killing spree, you'll come across Livvey, a Spacer who will plead for his life. How you deal with him is entirely up to you. Your companion, if you did bring one, will also say their piece about Livvey, but the decision is still left up to you. He also warns you about a puzzle right ahead, one that took out some of his Spacer friends.

Mantis Lair Puzzle Guide

Shortly after your encounter with Livvey, you'll find a puzzle with letters on the floor and four turrets primed and ready to blow your head off. You already know that “AM MANTIS” is not the answer if you've been paying attention to Livvey.

Spell out “TYRANNIS” by stepping on the corresponding letters to safely cross the room. This solution can be found by hacking into the Master-level Computer located in a cubby next to the puzzle room, pure bruteforce, or deducing it from the most recent Mantis' favorite quote: “Sic Semper Tyrannis”.

Tips for the Mantis Lair Puzzle

Crouch and switch to the third-person view to avoid accidents. Going on third-person view makes sure you always see where your feet are (the puzzle is not forgiving) while crouching reduces the slight momentum your character gets in third-person.

Quicksave right before attempting the puzzle to be safe!

Mantis Lair Rewards

After all of this (and beating a few more robotic enemies), you're free to reap your rewards. The Razorleaf starship is first – which has better stats in most fields than the Frontier ship you get at the start of the game.  It also has a Shielded Cargo Hold to hide your contraband in.

You also get the Mantis legendary gear set, consisting of:

  • Mantis spacesuit
  • Mantis pack
  • Mantis space helmet

Each will have one trait, giving it extra stats and bonuses.