Commander Shepard's story arguably won't benefit from Mass Effect 3 single-player expansions , but BioWare's willing to compromise if you buy the Leviathan add-on: Completing the downloadable content creates an additional rift in your ending. You can expect to see multiple Easter eggs, subtle changes, and references to its story when you reach the Extended Cut conclusion.

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Coming soon for $10, Leviathan's story content is accessible early in the Mass Effect 3 The question remains, though: Is Leviathan worth the hassle at all?Admiral Hackett's been running black ops on the hunt for an elusive creature known for killing Reapers. Nobody knows where The Leviathan is, but when a Citadel scientist called Bryson picks up the scent he's promptly murdered. His loyal assistant blacks out and puts a bullet in his chest, totally unaware of his actions. It seems like a simple case of indoctrination, but the deeper implication hints at something else. From there, Shepard makes his (or her) way through new part of the galaxy.I played a late-game mission aboard a ship soaked by aggressive waves and heavy rain. BioWare is conscious of fan demands to make combat more challenging, and Leviathan is unflinching. Cargo creates tight corners and small spaces aboard the boat, which makes it remarkably difficult to diffuse situations involving multiple Brutes aided by flanking Cannibals. The battle is tough, but Leviathan throws another curveball at you here. Because Shepard's trying to open a door, you'll need to carry power cells to a control point, charge the generator, and go back for another cell -- all while the power percentage ticks down to zero. It's a tense encounter with an unexpected new variable, and it pays off with access to a deep-sea diving mech.This is where Leviathan gets really interesting, apparently, but BioWare is coy about why.Shepard is desperate and reckless at this point in the story -- which is comparable in size to Lair of the Shadow Broker. He's flinging ideas at a wall to see what sticks, and plunging into the ocean in a walking robot is the plan he settles with. From here, you can explore underwater caverns populated by jellyfish and other aquatic life. What's down there to discover remains to be seen.Leviathan is, at any rate, an enjoyable new story segment in Mass Effect 3's elaborate tale. I'm still unconvinced it's necessary -- after all, my Mass Effect 3 story is over, I know how it ends, and I didn't need a Reaper-killing monster to help me out. I'm curious what difference it'll make, but not enough to replay the entire game.Will you start Mass Effect 3 from scratch to get through the Leviathan expansion?

Mitch Dyer is an Associate Editor for IGN's Xbox 360 team. He grew up two hours away from BioWare's headquarters. Read his ramblings on Twitter and follow him on IGN