You've got something worth some money, and he wants a cut. You could fight him off in court, but you just spent all of your money (and then some!) making the game. You can't make more money until you can sell the game and the Apple Store - not wanting to get caught up in the crazy business - won't carry it until you get this trademark business worked out. He waited until your game had hit the market but before you were able to recoup your investment, the moment when you'll be the most vulnerable. You can't afford to go to court with Langdell, and even if you did your game would languish for years until the case was resolved. Renaming the game will cost you, since you've built up a buzz around your game and gotten great reviews. You'll lose that momentum (and thus a lot of money) if you start over with a brand new name.
So you offer a compromise: You tell Langdell that you'll rename the game to "Edgy". The Langdell lawyers fire back and say "not good enough." Apparently Langdell not only imagines he owns a word in the English language, but he also owns all derivative words. This would be like Game Stop suing you for making a game called "Stopper". While you're standing there dumbfounded, Langdell runs out and trademarks the word "Edgy" for himself, just to be sure.
You probably figured out several paragraphs ago that this isn't a hypothetical story. Edge is real, and unfortunately so is Tim Langdell and his army of shock-troop lawyers. If you ever wondered why the Namco game "Soul Edge" was renamed to "Soul Calibur" here in the west, it's because of Langdell and his parasitical rent-seeking shenanigans.
Langdell founded Edge Games back in the 80's, although according to Kotaku he hasn't made a game in 15 years. His only contribution to the industry is lawsuits, trademark trolling, and name poaching. (He reportedly just grabbed the trademark for "Edge of Twilight," even though the game has been in the press for years. He also has a blurb for something called "MIRRORS, a game by EDGE" on the Edge Games site. He's obviously a lot more cagey when going after a leviathan like EA Games compared to his bullying of no-name indie developers.)
What can you do to save your popular little iPhone game that you worked on for so long? Maybe you could go to the International Game Developers Association. Their mission statement is "To advance the careers and enhance the lives of game developers by connecting members with their peers, promoting professional development, and advocating on issues that affect the developer community." Man, the IGDA sounds like exactly like the kind of people you need right now. Except that Tim Langdell himself is on the board of the IGDA, which is like having the Incredible Hulk as a member of The International Committee Against Smashing Shit Into Tiny Pieces.
If I'd been running Mobigame, I would have sucked it up and renamed my game from "Edge" to "Tim Langdell sodomizes the corpses of orphaned children who he may or may not have killed with his bare hands." It's not quite as catchy, but I'll bet Langdell didn't think to trademark it. On the other hand, I've never made a game and nobody has ever entrusted me with anything more dangerous than a pencil, so maybe it's a good thing I'm not coming up with titles for games.
Technically Langdell's actions are legal. Technically. It's also legal for a no-talent imbecile to stand next to a brilliant street musician and threaten to blow an air horn until the musician forks over 10% of their tips. You can get away with stuff like this as long as you don't mind being hated, shunned, and reviled by every decent human being in the civilized world.
The silver lining is that members of The Chaos Engine, a game industry professionals' think-tank/forum have started a fund to try and stop Langdell. This is way better than my idea, which was to wait for Langdell to be captured by space aliens who experiment on him to see how long a human can live on their own urine. Although either one is good with me.
Shamus Young is the guy behind this movie, this website, this book, these two webcomics, and this program. He's got a net worth of minus twenty thousand dollars, so he's not worth suing, Tim. You reptilian bastard.