XCOM: Enemy Within is more than an expansion for XCOM: Enemy Unknown. It's an entirely new level of alien infestation.

"Infestation" may not be the right word, though, unless you count harvesting alien tissue and technology to fuse with your own body.

According to Garth DeAngelis, senior producer at Firaxis, one aspect of the "Enemy Within" is the way players will use alien autopsies to create the expansion's two new brands of soldiers: mechs and genetic mutations, called g-mods.

These new soldiers, weapons, abilities and enemies were inspired by fan feedback and are a nod to player-created mods, bits and pieces of new stuff that fans have been clamoring for since XCOM: Enemy Unknown launched last October. But another way of looking at what the "Enemy Within" may be could be in the way players treat, or mistreat, these soldiers. You could be your own enemy, sending your characters off to die.

The death of player-created soldiers in XCOM wasn't meant to be intentionally humorous or dramatic, but as it would turn out, losing a character named after your boyfriend or mother is devastating.

"It makes sense for everything about this game, with consequences as one of our number one pillars," DeAngelis told Polygon. "And really, the challenge of the game, it makes sense to take away this mechanism or this piece of a game that we give to the player for good. That's very unlike a lot of today's games, where you just reload or restart, or the consequences go right back.

"We need to rip pieces away from the player that are permanent," he said. "I did name one [character] after my wife once, and I got flack for it, but I kept her on the back lines."

Players will have a wide variety of new things to tinker with, including new items, abilities and 50 percent more maps featuring new terrain like farms and urban sites. New goodies also include meld, a new resource that comes with a catch. Players can harvest meld and use it to make and upgrade g-mods and create new mech suits, but meld will only spawn in certain points on maps once for each playthrough. After a certain number of turns, the meld canister will explode, damaging any player units nearby.

"We need to rip pieces away from the player that are permanent."

Another new item available to players is a mimic beacon, which can be thrown on the map into a square within the player's moving range. The mimic beacon will send out a signal that tricks aliens into thinking it's human, drawing them towards it and anyway from any nearby player units.

During a demo of the game, I spent some time playing with the mechs and g-mods against a group of aliens in their own mechanical creations — mechtoids. Mech soldiers are especially powerful against these enemies because of their Kinectic Strike ability, which has the potential to do enough damage to blow enemies off the map. Mechs can also use Flamethrowers, a new weapon for Enemy Within. G-mods too have their perks: heightened versions of normal abilities like jumping and running. For example, g-mods can jump higher, scaling taller structures.

On the subject of assimilating alien parts, DeAngelis suggested that while the mechanic is a tidy way to tie the new classes into the game, players should think about the more ethical or emotional implications that come with it.

"You're taking these pieces of alien technology, and it's more so than just giving them to your scientists and engineering them, you're assimilating them inside of you to use against aliens," he said. "There's more to it than that, but I'll leave it at that for now."

DeAngelis also teased that easter eggs linked to 2K Marin's The Bureau: XCOM Declassified are scattered throughout Enemy Within — but wouldn't share where.

Currently Firaxis has no plans to launch Enemy Within for iOS, due to the already large file size of the original game for the device. For PS3, Xbox 360, Windows PC and Mac players, XCOM: Enemy Within will launch on Nov. 12 in North America and Nov. 15 worldwide.