I have to say that lane defense (i.e. games like Plants vs Zombies) and MOBAs (i.e. games like League of Legends) aren't exactly a combination I'd ever pictured before. But that's kind of what Rumble Entertainment's Nightmare Guardians is: a lane defense MOBA.
Unlike a typical MOBA (aside from the lane defense thing), Nightmare Guardians isn't about teams fighting other teams but rather a few players cooperating to fight off increasingly tough waves of enemies. Of course all the focus on special abilities and skills is still in there, and you can upgrade and swap out skills before each game. It's a pretty interesting and quick co-op game, really.
Nightmare Guardians will be hitting the App Store in late summer as a free download.