Not much is to know about this mystery girl.  Her first episode was the Season Three opener "Into the Moonless Night," she was sent to Mutant X as damage control after Adam disappeared. Lexa would lead Mutant X in the right direction in missions, but not anymore because it turns out that the Dominion were the bad guys.  In one word Lexa would be described as "unpredictable".  She has shown some affection for Jesse (of course, I mean, the guy's a big teddy bear). Throughout the season she proved that Lexa knew what she was doing and is probably a good fit to the team. 

Whatever you read on different sites it's going to be possibly the exact same thing because we really know nothing about Lexa except for what the episodes give us, I got most of the information about Jesse, Shal, and Brennan from the Genomex faux site. But let's put her life in her perspective. You're mid to late twenties, you've been searching for your brother for almost 5 years, and the only way you can find him is if you join three other mutants in a cave who don't trust you except for maybe ONE person, you find your brother only to lose him again to save possibly the only person that would probably not do the same thing for you, and then you're getting used to living and working with those other 3 mutants right before you might go to war with the people who helped you find your brother in the beginning. What would you do? Not the most difficult decision she made: Take the Dominion down. But other than that; here's some information I got so far:

Mutant Classification: Molecular (she is the same type as Jesse, but her abilities are different) 

Powers: light-Chromatic, or Lexa can manipulate light (lasers, beams, etc Bend light around her so she can be invisible)

There's been discussion about who has evolved in character throughout season 3 and almost everyone has agreed it's Lexa. In the beginning, Lexa trusted no one, was completely cold, and was reluctant to risk her life for anyone. But as the season went on, she trusted her teammates, warmed up completely to everyone, and was willing to give her own life for any of her team. She's made a complete turn around, and I think we know who to thank for that .... no, it's not Peter Mohan (head writer) it's the one and only Karen Cliche. She said herself in an interview with PureMX that she had thought Lexa should have warmed up by now, and she made a choice to change Lexa's attitude. What a great choice, huh? I was a fan of Lexa before, of course, that kickass attitude, great powers, and funny sarcasm was a recipe for a great character but without this, what me and LilLex call a new-and-improved Lexa, we'd probably never have those great Lexa-fluffy episodes like Dream Lover and those dramatic-Lexa episodes like She's Come Undone and Cirque Des Merveilles... of course, we have to give Mohan some credit, I guess ... but only some. Lexa truly has grown into a loveable yet still a sarcastic and funny character. Hopefully, this isn't the end for Lexa because T.V. wouldn't be the same without her.

This was originally going to go in the Thoughts&Theories, but since it's about Lexa (Actually, Lexa's powers) It's going here.

Lexa's Invisibility

There's been a lot of discussion about Lexa's abilities, mostly her invisibility. In the Genomex faux site, there is only one classification of mutants that have the ability to become invisible: Stealth mutants. In Season One, we came across a Stealth Mutant named Danielle Hartman in the episode "Whiter Shade of Pale". In a special scene where Emma asks why Adam keeps referring to the mutant as a "Stealth", he explains that Stealth mutants' abilities aren't quite like "H.G. Wells' Invisible Man." That Stealth Mutants create a shield around themselves that reflects light to make them invisible. Flash forward to Season Three, "Into the Moonless Night," when Lexa reappears in Sanctuary and then disappears. Jesse explains that she was "Bending the light around her" ... Instead of making a shield around her to "reflect light". Which is different from Adam's explanation in "Whiter Shade of Pale". Also, in the Genomex faux site, there is a classification called Chromatic (light, color related) which we have guessed that Lexa is a light Chromatic Molecular. If she does control light, then she can perform this "bending" using her abilities. So to make sense, Lexa is not a Stealth but a light-Chromatic.

Lexa's Lasers

There has been thoughts that Lexa could be an Elemental-Molecular hybrid, explaining her lasers. I guess that's a possibility, but Lexa has the ability to control light, or to put it in scientific terms she can control the direction of light waves but more importantly Lexa can polarize light waves (cause them to vibrate in different ways). She can definitely cause light to vibrate sharply creating lasers. For you to understand this, you have to know that light comes in waves, the wavelength is the measure between the tops of the waves and lasers have very small wavelengths and the flashes that Lexa does have very large wavelengths, which explains why no one is burned/hurt when she sets them off. If Lexa can control the vibration of light waves (which means if she can control the size of the waves and wavelenghts) she can definitely shoot off lasers with her fingertips. Those are just my thoughts on her abilities, however, because I have no proof that she is only a light Chromatic and not a Stealth/Elemental-Molecular hybrid. But I believe that I make very valid points.

In the PureMX Boards, we've been having a discussion/debate about Lexa's entrance and why the other teammates accepted her so quickly, and didn't ask her to leave. I've asked a few members if I could quote them for this part of Lexa Xone and they've agreed. Here's what they had to say:

--------------------------------------------------------------------

Impulse: Lexa didn't want to be there, the Dominion made her go there[Sanctuary], and then suddenly, they tell her she has to stay. Hell, I'd be mad too.
LilLex: I think this is the point everyone's forgetting. She didn't plan on being nice or for waiting to be accepted. She thought it would be a temporary assingment and she'd be gone as soon as it was over. But they made her stay and sort things out there. The Dominion kind of told her to take charge and bring MX back together. So she was pretty much just following orders.
Impulse: That's right, she did say something in Into the Moonless Night about running a mutant half way house or group therapy or something.
TheMuTantXFreAk: She DID want to be there...she wanted to find her brother.
Impulse: Actually, no. She worked for the Dominion so she could find her brother, so, they told her to be with Mutant X or they wouldn't help her. She did what she had to do to find Leo.
LilLex: Yes, that's what she told the Dominion. "This wasn't part of our agreement. This was supposed to be a temporary arangement." or something like that. And he told her that he would only help her locate the person/persons she was looking for if she did this. She did not want to be there. She was forced into it. She didn't have a choice.

First Mutant: I suppose I'm the only one here who wasn't shocked by the team's following Lexa's orders. I always saw Emma as the stabilizing influence on the team, and Adam as their cult leader. Emma's death and Adam's disappearance occur simultaneously, so that Jesse, Shalimar, and Brennan find themselves suddenly cut adrift from their fearless leader and the member that keeps them grounded. Are they capable of independent thought? Can they survive in the real world on their own? Nope.
Like confused and frightened sheep without a shepherd, they turn to the first authority figure that steps up to the plate--Lexa and the Dominion. She's smart. She's beautiful. She simply exudes self-confidence. Her name is in the computer. She has a cool ring. She knows where the Jello is (a.k.a. "The Aura of the Smooth," Onychomys). But there is more than this. Most important of all, Lexa comes to these lost kids with A PLAN! She is allowed to step into Adam's shoes because she and the Dominion hold the holy grail: a slew of ready-made missions which represent a purpose, a reason for being.
Background checks might reveal that the Dominion and its operative are not what they appear. Then their purpose would be lost, and they would be cast adrift again in a sea of uncertainty. Why take that chance? Safer to simply do as they're told, even though they don't like Lexa personally. Shalimar never considers Lexa a friend, even by "The Prophecy." Brennan's still questioning her loyalty in "The Assault." Don't like her, don't trust her, but follow her anyway because these children need direction; any direction will do. Without Emma, they never stood a chance. Lexa's lost her trust in people, and so has a prickly outer shell that repels her teammates.
My point is more that, while Shalimar and Brennan follow Lexa, they do not open up to her or welcome her easily. They do as she directs, yet Lexa is barely tolerated as a member of the team, and is not perceived as a true member of their inner circle as Emma was. I'm proposing that the reason for this seeming contradiction is that they accept her authority not out of love or trust, but because of their all-consuming need for a new cult leader--someone, anyone, to give them direction. As long as the children remain children, they will always have need of a babysitter. Shalimar, Jesse, and Brennan are grown-ups in age only; somehow their mental maturation was stunted along the way. Perhaps it's because Adam took them in when they were teenagers, and they have not had to do any independent thinking since.
I agree that Adam was their father figure, but he was not a good one. I don't doubt that he cared about his team in his own way, but the strength of his ego was simply too overwhelming to allow them any opportunity for developing independently of himself. Working alone on missions not related to Mutant X, establishing friends outside of their close-knit group, living outside of Sanctuary--these activities were frowned upon. And yet, venturing out into the unknown is how teenagers learn, separate from their parents, grow up into adults.
Having missed these opportunities, Shalimar, Jesse, and Brennan need Lexa as their babysitter, and the Dominion as a source of income. If they kick Lexa out, they lose the Dominion's support, along with their allowance, and room and board. They might have to *gasp* get jobs! And what jobs would they be skilled for? Sanctuary's monthly electric bill alone would certainly overwhelm the salary of any McDonald's employee. And how would they pay for the essentials: video games, fuel for the Helix, Jell-O, Chinese food, and tanning beds?

LilLex: Perfect FM, I could not have explained it better myself. You've got it!

-----------------------------------------------------------------

There's been lots of speculation about Lexa's importance and entrance, but as First Mutant blatantly said: Lexa was the "shephard" in Mutant X because the other 3 didn't know what to do.