This one is building up for a long time now, I just didn't felt to start a flame war.
So, I think Miss Martian will be an antagonist in the future. She might be the creepiest character on the show, and we all saw Desaad. Why? Let me go back to her first appearence. She started as a naive, sweet, if somewhat annoying girl, with a huge crush on Superboy. I liked her, though she had her... off moments. Like the time she asked Superboy, to help her out in the kitchen, and... well, what the hell you think happened? I'm not implicating anything, not yet, so moving on. Next stop, Byalia. I'm not the first one to point out, how she left Aqualad to his fate, and charged out, to save her crush. Justifiable? She could just as easily pointed to Sb's direction, and save Caulder. Did she got a though talk about that? Maybe. But the hole thing started to show how obsessive she is. Then we witnessed, that she is capable of subconsciously mess with the team's mind, including her own, not to mention Manhunter's. By far the most powerful telepatic power on the planet. Possibly in the galaxy. And she is an obsessive teenager, to whom lying is a second nature. Totally not frightening or anything.
But moving on. There was that weird moment when she revived her own memories in Byalia, when we saw her in a cheerleader costume, with a laughtrack. That bugged me until the episode which shown us the comedy show, from which she borrowed her appearence. And her persona. And her fricking boyfriend? Ok, the series was an escape from her grim reality, as a minority. She kind of looks like the actress playing Megan, and... holy union, she is a shapeshifter, not even remotely resembling a human, who just took the form and personality of a fictional character. and the second she saw Superboy, she changes her costume, and from then on, it is painfully clear, she is in love. And Connor? Reluctant at first, even antagonistic, then slowly he thaws up for her, and finally succumbs to his feelings... Wait a minute. I just typed "slowly", though it really happened in just a little more than two months. So, she meets Psymon again, and we saw her true form, and what she fears... and then she tells us, that she would do anything, to prevent things coming to light. Bam, she sends Psymon into a coma for years, and starts the lying again. Untill her boyfriend comes out with his rather ugly secret, which followed by her teammate coming out, and just then she shows her true form. It's okay, though, at least she did it. What a relief to her, and Connor telling him that he knew? Must have been a fantastic, reassuring moment.
Season finale, overpowering Manhunter, in like a second... Mind you, he is, in every previous incarnation is a monstrously powerful telepath.
So we are here at second season, seeing how she casually turns thinking beings into vegetables. The only one confronted her was her now exboyfriend, who dumped her after he caught her messing with his mind. And who said it was the first time? Certainly not me.
But the last thing made me sure about her creepiness, is the part, when the leaguers left to their trial. Did anybody noticed how weird Manhunter sounded? And watering plants? Really? He witnessed what Megan did to that crolotean. Remember his face? Also, Batman was present too. I like to give him a hard time, but he is not that dumb. So either the League is totally okay with this kind of interrogation, or she just deliberately alters their minds, when thing go south for her. Maybe she is doing it subconsciously, maybe not. But she is doing it, of that I'm sure. Oh, almost forgot another suspicious scene: in Alienated, she and Manhunter are waiting on her bioship, in crolotean form. When Lagoom Boy arrives, she is all Hello Megan! again, saying "(I) knew we forgot something". Then they change back simultaniously. Knew we forgot something. Not unsettling at all.
She might not even be Martian Manhunter's niece, what with not being from the same race, and everything. Ok, maybe the Jon'zz faily is an expecting, tolerant bunch, but honestly, after all the things she did to this point, I can totally imagine her lying about that too.
Please, understand, I do like her being on the show, she is a great character. I just think she is a horrible person, who is already on the path of supervillany.