The next Orcs Must Die! game is something a little different. The original is a single-player-only hybrid of third-person action and tower defense with a great cartoony art style; the second is the same formula with two-player co-op and deeper customization. Both are amazing, and if you haven't tried them, you should! Now, developer Robot Entertainment is taking the series competitive and free-to-play with Orcs Must Die! Unchained, a 5v5 multiplayer game (with solo and co-op vs bots!) for the PC that fuses the OMD! action, strategy, and style with elements of both MOBAs and customizable card games.

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“We’ve been calling it a fortress siege game,” Robot CEO Patrick Hudson says, explaining the simultaneous attack-and-defend flow. Picture it: instead of just defending against waves of enemies with a maze of gleefully sadistic traps, you get to do that and lead waves of AI allies into head-on battle in an effort to push through someone else’s sadistic traps to reach the other team’s fortress.

“ Which guys you send on which paths and at what time, is the decision you’re making.

“ None will be locked behind a paywall.

By the time of its anticipated launch in late 2014, Robot plans to offer dozens of playable hero characters on two factions: humans of the Order (which has been rebuilt by the War Mage and the Sorceress after OMD2) and the new monster heroes known as the Unchained, who’ve emerged from newly discovered rifts. Each hero is designed with a role in mind, such as offensive melee-focused characters, “leaders” that buff minions, support characters that buff other heroes, defensive classes that can improve traps, and more. Most characters will have at least some ability to sabotage enemy traps to help their minions.The fiction presents the Unchained as the Order’s adversaries, but while Design Director Ian Fischer says they’d experimented with segregating the teams along faction lines, in the end they decided it was more fun to allow you to mix the factions and let teams play as both Order and Unchained in any combination.Which equipment and minions you’ll have access to in a given game will be based on which virtual cards you’ve unlocked and what you’ve loaded into your deck before you start. “We took Spell Book idea for that and used it as the basis for what we’re doing with the cards,” says Fischer. “It’s not just traps, because we have offense in the game now too. All of the things we have set up for the hero, we use cards for. It’s traps, it’s minions, it’s equipment on your hero, it’s Weavers.” None will be locked behind a paywall, he promises.On the decision to go free-to-play, Hudson is blunt: “You’re not going to get people paying for downloads in Asia and Russia,” he says. At the same time, he says they’re being very careful about pay-to-win scenarios. While it’s too early for Robot to specify exactly how its free-to-play transactions will work, Hudson says they’re inspired by Riot’s free-to-play model in the extremely popular League of Legends. While not quite as generous as Valve’s Dota 2 free-for-all, it has earned lots of fans with a regular rotation that temporarily makes paid content available for free.If you’re attending PAX East, be sure to keep an eye out for Robot and Orcs Must Die! Unchained’s playable stations on the floor. (We're definitely going to swing by and give it a shot!) If you’re not, the only way to play it before it comes out late this year will be through the buy-in Founders program , which launches today.

Dan Stapleton is IGN's Reviews Editor. You can follow him on Twitter to hear all about how awesome PC gaming is, plus a healthy dose of random Simpsons references.