Backstab Gaming Protocols is a PvP variant of Invisible, Inc. which can be played either between two players as a one-shot game, or in a knockout tournament format.
Mods required:
Start from a save where the required agents are on the team, with Seed + Golem + Emergency Reserve, in Endless or Endless Plus mode, with the extended campaign disabled, 0 starting money, allow melee while seen. Level retries are enabled in order to keep going in case nobody survives a mission, and 99 rewinds for use in case the Operator makes a mistake inputting an action.
The game is played in “battle royale” mode, using the the Encroaching Danger mod, which means sections of the map gradually become “danger zones” throughout the mission, with penalties for agents who end their turn in those areas (yellow = -2 AP; red = -4 AP, no attack, alert nearest guard). This encourages players to keep moving forward, and should eventually trap them together in the exit room to prevent a stalemate.
If a player has both agents still alive, they can choose which one to bring into the mission. One of the two players (decided by coin flip) chooses which mission is selected, and has control in the mission first. Each player can freely move items between their own agents before entering the mission (of course, if you give everything to one agent, then you won't get your stuff back when they die, so your second agent will be SOL…).
Instead of enforced turn order, you can “yield” to the other player after taking some actions. You may instead “end turn” if you have only made “free” actions (toggling ambush/overwatch, doors, or power supplies; in this case you would “end turn” instead of yielding. If you have less than 1 AP left, then you *automatically* end turn as soon as you are yielded to.
If you have control and one of your actions causes your opponent to be overwatched by a guard (armed drones/turrets count, null drones don't count) during the player turn, then control is automatically yielded to your opponent, even if you are also overwatched at the same time. This rule does not apply if your opponent was already being overwatched by a different guard (or turret) before your action.
You are not allowed to transfer items between your agent and your opponent's agent. However, you are allowed to loot your opponent's stuff after they are dead. You are not allowed to give items to guards or put them into safes/other containers.
Shared resources (PWR, money, Incognita, items left on the ground, hacked drones, Courier/Prisoner) are a free-for-all. When you have control, you can do what you want with them, except you are not allowed to sell Incognita programs. If a detention centre mission is chosen, and the prisoner is an agent, you are not allowed to free them. As an exception to this rule, only the player controlling Derek may activate his Transport Beacon, but the other player is allowed to pick it up from the ground.
Agents are not allowed to step on the 2×2 teleporter tiles in the exit room until the other player is eliminated, nor are they allowed to throw items onto these tiles. You are not allowed to close doors after alarm level 5. (This is to prevent door-cheesing in the exit room.) You are not allowed to step through an enemy-controlled Beam Emitter (laser which raises the alarm) more than once in the same turn, or when Authority is active access the same safe more than once in the same turn.
If an agent ends their turn blocking a chokepoint, then that agent is not allowed to block the same chokepoint on the next turn. A chokepoint is defined as a contiguous set of tiles, each of which if deleted would locally disconnect the revealed map; if an agent ends their turn in a chokepoint, then on the next turn that agent may not yield or end turn in that same chokepoint, unless there is no legal action the agent can take to avoid blocking. For the purpose of this rule, locked doors are not valid paths, even if one or both agents would be able to unlock them; and enemy-controlled lethal Laser Panels are not valid paths even if one or both agents would be able to disable them or pass through them. If a chokepoint was blocked by a rescued Courier or Prisoner on the previous turn, then it is OK to yield/end turn with them still blocking, as long as they still have enough AP for the other player to move them out of the way. It is always permitted to block a chokepoint using a hacked drone.
You may only leave the mission when the other agent is dead (or KO'd and pinned - pinning with a hacked drone doesn't count, but pinning with a rescued courier/prisoner does count, as long as they survive long enough for you to escape the facility). You must leave without the other agent - no dragging their body into the teleporter.
Once the other agent is eliminated, you are no longer allowed to loot safes, steal from guards, buy/sell items/augments/programs, do objectives/side-missions/etc, use an Econ Chip, exfiltrate a rescued courier/prisoner or refit drone, fish for Fortune, or (if you are Draco) scan bodies/corpses. You are allowed to pick up items from the ground (including deployables/throwables), and you are also allowed to loot items from the other agent after backstabbing them.
Once you are eliminated, you are still allowed to use shared resources to try to save your agent if they are KO'd, but not if they are lethally wounded.
If neither agent is eliminated by turn 50, then the mission is ended using debug mode, and the round is replayed in another mission. In this case, the “no looting” rules apply for the whole of the replay mission.
If the game reaches day 5 so that you need an exit card to leave the mission, then one will be debug-spawned on the tile in front of the exit door once the exit door is found and the backstab is complete. It is not necessary to find the exit card in the safe, but if you do find it then you are permitted to open the door early.
When played as a double-elimination tournament, there are some extra rules:
After the mission, the winner can spend whatever money is available on upgrading their agent(s), including buying from/selling to Monst3r.
In a mission if both players' agents are lost, then both stay “dead” for the purpose of the tournament. If both agents die, then debug mode is used to instant-win the mission but the game is a tie, and both agents count as eliminated for the purpose of the tournament. Whoever would have been the winner's next opponent gets a “bye” for the next game and is entitled to spend any winnings from the tied round themselves.
If the last two remaining players both die and this would end the tournament (i.e. at least one player is on their last agent), then the game will be replayed using a level retry. In the “final round” of the tournament, you still need to make it to the exit after killing your opponent in order to be the winner.