Despoina: Leviathan

The shuttle has been disabled by an unknown energy surge. Search for Leviathan and find a way to escape the planet.

Walkthrough
The mission begins onboard the shuttle, where you discuss amongst yourselves how a probe you sent has managed to pinpoint Leviathan's location and how you're supposed to reach it. One of your squadmates will express doubts on bringing Leviathan to aid in the war, and you can answer whichever way you want.

While descending on the ocean planet the shuttle will be disabled by a mysterious pulse. Cortez manages to set the shuttle down at one of the floating wrecks littering the ocean for repairs and you will have free rein of exploring the immediate surroundings. There's a bunch of datapads by the makeshift shelters along with some items worth picking up for credits. You will also see mysterious spherical artifacts inside some of the shacks and containers; they can be shot at.

After a short interval one of your squadmates points at something in the sky. A Sovereign-class Reaper is descending. Reaper forces start pouring in, beware of Brutes. Deal with them until Cortez manages to complete repairs and starts providing air support.

It turns out Cortez cannot stay airborne for long due to being hit again by the pulse so he lands the shuttle at the other side of the wreck. Deal with the Reapers then go over and talk to Cortez for the next part of the mission. If you haven't managed to get all items in the first pass due to having been interrupted by the Reapers's arrival, now is the chance to backtrack and get everything missed. Don't forget to take note of the M-560 Hydra by the supply stashes near Cortez, the medkits, and the Kodiak.

You ask Cortez for the Kodiak's status and he replies that it's inoperable. One of your squadmates suggests pickup by Normandy, and Cortez points out the same thing will happen to the ship. Since it's impossible to go airborne or be rescued until the problem goes away you will resolve on pressing forward: find Leviathan. Cortez suggests using the Triton mech stored inside a section of the wreck. Since the door to it is sealed, you need to get it open first. To that end, several power sockets are scattered throughout the wreck and Cortez suggests using the shuttle's power cells to give the necessary juice for opening the door.

Reaper forces start landing en masse again. You gain a backpack containing the power cells and you have to bring them to the sockets, stay alive while the cells are being loaded, and come back to Cortez for more until the door finally comes open. One of the sockets is near the bay door itself, and another is at the seaward side of the wreck in front of the door. You face a multifold problem here: the energy in the sockets is slowly dissipating, necessitating the need to finish as quickly as possible, and you will face lots of interdiction from Cortez to the sockets. A good time to use the Hydra is when you're nearing the 100% mark and there are Brutes in the way - a panic button, if you will.

Once you get the door open you must use the Triton to clear out the enemies: Reapers keep falling if you insist on taking them out conventionally. You may think you've cleared out a "wave", but the Sovereign-class Reaper overhead will simply drop others to replace what you've killed. The Triton handles like an Atlas, use your favored moves for dispatching enemies with the mech. Hordes of Brutes will spawn to test the Triton's mettle so be ready accordingly. When the enemies are dealt with walk the mech over to Cortez so he can run a systems check on it.

When Cortez proclaims the mech ready to go, you will have a choice between diving immediately or holding off first. Now is the absolute last chance to go through any items that may have been missed if you choose to procrastinate. You can always talk to Cortez whenever you are ready.

Partway through the dive you will begin to lose contact with Cortez on the surface - some kind of interference is cutting you off. You will spend the remainder of the mission alone on the bottom of the ocean. Take time to enjoy the surroundings, the Triton will helpfully fire flares in order for you to find your way around. You will keep going down until you come across the probe you sent earlier. Walk the mech over to it, then it shoots another flare in the distance. A rumble will issue from the chasm not far from you, go to it and prepare to meet Leviathan.

The entity you're talking to will detail its reasons for staying clear of the war. It will give you an outline of its race's history and you can ask it questions critical to the story. When that's done the Leviathan declares that you must remain with them while the Reapers harvest the rest. It's your job as Commander Shepard to convince it otherwise, and it will accept due to its own reasons.

You will engage the Triton's emergency boosters for the ascent and on the surface you will see the fruits of your conversation with the Leviathan: a Brute will turn against another and start messing with other Reaper forces, and while you escape in your miraculously repaired shuttle the Sovereign-class Reaper shows up trying to block your path when the pulse that disabled the Kodiak earlier hits the Reaper, causing it to crash into the ocean.