Halo: Reach is doing it. Gears of War 2 popularized it. Even Modern Warfare 2 (sort of) did it. Now BioShock 2 is getting into the scene, too. Its upcoming downloadable Protector Trials, due out August 3 for the PS3, 360, and PC, has players taking on waves of A.I. baddies, similar to the "Horde modes" we've seen rise in prominence in the last couple of years.

For being one of the most original game series around, BioShock has no trouble following the herd (a lot of people wondered why the last game had to include multiplayer, which has a Modern Warfare-like -- and -lite -- progression system). But whenever it seems like BioShock 2 is jumping on the bandwagon, the developers surprise us by taking charge and making these modes their own -- well-integrated into the universe, its themes, and the gameplay itself. On the surface, it may look "me too," but a little bit of playtime reveals these are as BioShocky as anything in the main games themselves.

In BioShock 2's multiplayer, for example, you don't just run around and shoot, shock, fry, and freeze opposing players. You can hack vending machines to set traps on them, or you can photograph your downed foes to get bonus research damage on them when they respawn.

Similarly, Protector Trials doesn't just have you mindlessly fending off throngs of Splicers. Like in the campaign, here, you play solo as an Alpha series Big Daddy (not the same one from the singleplayer story, though) who must protect a Little Sister as she's milking a corpse of its power-giving Adam juice.

These aren't straight rip-offs of similar scenarios from the campaign mode, either. In each of the 18 total trials spread out over six different environments from BioShock 2, the designers have handpicked different sets of guns and plasmid powers for you to enter battle with. "There are very different loadouts," says Ryan Mattson, lead designer on Protector Trials. "They progress from more accessible to ones that are a lot more specialized and specific."

One trial, for example, might only give you trap-based weapons and plasmids, like trap rivets, trap spears, proximity mines, Cyclones, and Decoys. The enemies don't come out until after you've set Little Sister down to do her wetworks, so you have all the time you need to set up an intricate web of pain. This won't leave you confident for too long, however, because after the Splicers start creeping in, you'll realize you only have these trap tools to work with for the rest of this round -- it's much easier to set them up beforehand to snare incoming enemies than to use them to kill active targets.

Other loadouts may be more straightforward, with all power weapons or gear for more intimate encounters (with a tonic-boosted drill as your primary means of attack and Insect Swarm as backup), or they may be more hacking- and repair-oriented setups, with many combinations in between. The idea is for you to play each level in unique ways...to experiment with the variety of gameplay that BioShock 2 offers.

In each stage, you'll find first-aid stations and several vending machines which you can hack before you start. BioShock players know Splicers can use those health boxes, too, so engineering them to poison everyone who is not you is key -- if you damage an enemy enough to send it off running to heal himself, you can turn your attention to higher priority concerns, knowing that station will likely kill him.

A hacked vending machine gives you a discount off of health/Eve supplies and ammo (specific to the current loadout) that you can buy in the heat of battle. You don't start with any dough, but you get some from killing Splicers. And in a little arcadey twist, you actually get a multiplier to your earnings the longer Little Sister goes on extracting without any enemies interrupting her. So for more cash and a higher score and rating, you have to keep everyone off of her at all times. "Getting the best score you possibly can," says Mattson, "is about understanding and mastering all the BioShock 2 tools and how they interact together in all these different loadouts."

Protector Trials certainly adds a very specific BioShock flavor to the traditional Horde mode, but it may be too similar to what's in the campaign already for a lot of fans' tastes. But with the different loadouts providing gameplay variety and a very friendly price point ($4.99 or 400 Microsoft Points), this is a compelling way to jump back into the dangers of Rapture.