Subject 617, also known as 'The Hidden', was a secret genetic experiment by British scientists at a research lab known as 'Infinitum'. The research conducted by these scientists was based on DNA manipulation which revolved around human test subjects, most of whom lost their lives. As the failure rate for these test subjects decreased, the scientists furthered their research; looking into Biological Light Refraction. However, due to miscalculation errors a series of test carried out on Subject 617 led to 'Synaptic' trauma, leaving the subject with genetic anomalies.
Eventually, Subject 617 escaped, killing anything and everyone that got in its way. As a result,I.R.I.S. (Infinitum Research Interception Squad) have been deployed to help recapture the failed test subject 617 for further experimentation.
One person is selected to play as Subject 617, they are equipped with only a knife and two grenades however they are almost completely invisible, extremely fast and have the ability to jump very long distances. Subject 617's other abilities include pouncing, wall grabbing, corpse pinning and the fatal pigsticker attack. His job is to take out each member of the I.R.I.S team.
Pigsticker - Your main attack as Subject 617, you activate it with your right-click and it has a long wind-up time. There are two ways to judge the strike window, the growl of Subject 617 as well as the animation. The animation is the best option, but it has a tendency to bug and not animate, which leads you to only having the sound to guess when to strike. You can combo the pigsticker with a pounce move to get in close just as it strikes, but that it a more advanced technique that requires a relatively low latency.
Melee attack - This is your left click attack, which can be used to finish off low HP opponents. It isn't advisable to attack a full or high HP I.R.I.S. member for fear of their reaction and immediate backlash, which would harm you needlessly. The point of using the melee attack is to be able to harvest the body afterwards, which would be pointless if the health regained only replenished the health lost in the scuffle.
"Hidden Vision" - Essentially detective vision, activated with "C", it can be used to see through a layer of wall and will highlight the I.R.I.S members with a color hue representative of their current HP. This is extremely useful but can only be used when standing still and depletes your stamina while doing so. Use this sparingly as you land from your pounces to track the squad's position and pinpoint places of weakness where you can prime your pigsticker and jump in for a moment before disappearing.
Homemade Grenade - The stun grenade, of which you get 3 per round, is another essential tool to getting rid of I.R.I.S. as well as punishing members that huddle together. The explosion will also effect yourself, so don't jump in before it detonates, or it would be pointless and you would be disoriented as well. Though the grenade wasn't meant for it, you can kill with two or three well placed grenades to an squad members feet or chest, and they will explode as if they were pigstuck. Using this to scatter the squad is also a very easy technique that will jitter most squad members and cause them to be a bit more erratic, allowing for your quick entry and exit from their bodies.
The I.R.I.S team is made up of every other player who isn't the current Subject 617. The object of the I.R.I.S is to take out Subject 617 before he takes out them. They can only see the silhouette of him and will need to co-operate well to take him out. Whoever gets the final bullet on him becomes Subject 617 in the next round.