I know a lot of people hate the Domination system in TF2, but it really does strike me as a particularly worthwhile idea I’d have definitely tried were I one of the initial developers of TF2. There’s no better way to teach somebody that they need to beware of specific enemy players, and before the time of cosmetics it was a clever way to differentiate who you’re shooting at by adding characterization to a single notable enemy.

For memories' sake, here's Jigglypuff killing me with my own sword. I'm going to miss you 'Head Launcher"...
Especially if they kill you with your own weapon. Then they’re characterized as an asshole who’s nevertheless way out of your league.

In a multiplayer shooter, I think it’s a particularly interesting challenge to try and visually separate the enemies so they don’t all look the same. I’m not really talking about cosmetics, even though cosmetics absolutely fill that role. I mean get the player to interact with his opponents in such a way that they humanize specific opponents. TF2’s idea of branding the dominator with a little in-game symbol is honestly pretty unique and I can’t think of any other game that broadcasts a domination so strongly. There are games that reward you with bonus XP for killing a player who’s doing well, like League of Legends, but you often have to kill them to find out, and then its more of an unexpected but welcome surprise. TF2’s format turns a successful player into a specific target, a nemesis who suddenly made the battle personal. Counter-Strike is the only other franchise I can find that has a system that comes close, and its restricted to non-competitive game modes and only shows up on the HUD and killcam.

Of course, TF2 also has a second, opt-in way to single out specific enemy players, the Dueling Mini-Game that was supposedly ‘the first [mini-game] we’re shipping‘ but nothing else ever arrived to replace it. (If I had to suggest something, maybe an “Objective Completing Mini-Game” you could challenge your teammates to, thus encouraging them to actually play to win. Alas.)

Upon both players accepting, the two will see a ‘crossed-pistols’ icon floating over each other’s heads, and their frags on each other get tallied for the remainder of the round. Then, when the round ends, whoever has the most earns another tick on their dueling badge. For the most part, this mini-game is completely ignored and didn’t really captivate anyone’s attention except Johnny Kickass, who won the related Per Diem hat day after day in the TF2 beta by being the only person buying (and then using) the dueling mini-games Valve gave everyone for testing. In the actual game, I honestly think the price of the action item was the main thing stopping people from initiating duels; I certainly didn’t want to buy a thing that burnt itself out after a mere 5 duels. It didn’t help that the Dueling badge was just a reskin of the memetically unremarkable Mercenary badge. Overall the mini-game needed more of a reward for partaking in it.

Planetside 2‘s bounty system is the first thing that comes to mind when looking for a similar system in another game, though this time it’s perfectly legal (and in fact, almost certain) that your teammates help out in murdering your target. For a mere 50 certs you can mark your last killer with a bounty, causing them to appear with a special icon on the mini-map and warning them of their new status in the chat. Once somebody eventually kills them, both of you get an XP reward, and until then the hunted player can get bonus XP for increasing their killstreak without dying. I adore the system because It’s a win-win-win for everyone involved, and a cert sink for the developers.

All in all, I think more games should add these sort of systems. Interactivity is the name of the game in shooters, and promoting identification among players, even between those on opposite teams, can only increase the investment in their shared experience.