Multivariate Cooperation (M.C.), commonly known as Co-op, is a co-operative multiplayer game mode in Arknights.

Overview

In M.C., two players must work together to clear an operation. As such, teamwork and coordination is essential to ensure success in M.C. operations; both players' actions will dictate whether the operation is a success or failure.

M.C. operations do not use Sanity to run and are established through a matchmaking system with three options:

• Create: The M.C. operation's difficulty and map, which position the host will assume, and whether the operation is open to everyone and the host's friends are determined by the host.
• Search: Searches for and joins another player's M.C. operation.
  • If the operation is open to the host's friends and the player is one of the host friends, then it can be joined right away.
  • If the operation is open for everyone, then it must be joined by entering its Project Number.
• Match: Pairs the player with others in M.C. operations whose difficulty, map, and position matches the player's setting.

Operation

M.C. operations have three difficulties: Normal Test Mode, High-Pressure Test Mode, and Challenge Test Mode. The Challenge Test Mode difficulty is available after the M.C. operation is cleared in High-Pressure Test Mode for the first time.

• Normal Test Mode: The baseline difficulty.
• High-Pressure Test Mode: There will be more enemies with some being replaced by the upgraded versions (e.g. a Senior Caster may be replaced by a Senior Caster Leader).
• Challenge Test Mode: Same as High-Pressure Test Mode, but with even more enemies and more upgraded ones, in addition to featuring handicaps like in Challenge Mode (as the name suggests).

Before playing M.C. operations, the player must create at least one squad to be used in the operation; there can be a maximum of six squads for each M.C. operation. Note that the squads can only be edited outside M.C. sessions. While in the M.C. session's lobby, players can communicate using emoticons through the Team Meeting function, with the host also capable of removing the other player from the session or to terminate it altogether.

Each M.C. operation consists of two layers: the Upper Level Test Area, or "upper", and the Lower Level Test Area, or "lower". The player's layer is determined in the lobby and cannot be changed once the session starts, and each player has their own DP and Unit Limit count. A player may view the other player's layer, but cannot deploy units there. While viewing another player's layer, access to a "ping" tool is granted, allowing the player to mark specific tiles on both layers to notify or alert the other player; the marking function can be used three times in sequence, after which a short per-charge cooldown is instated.

Enemies on the upper layer will eventually move into the lower layer via Tunnel(s) linking both layers; the Protection Objective(s) are located on the lower layer.

The upper player may also provide support to the other player with the map-specific static devices which always have an upper and lower part; the upper player must deploy units adjacent to them before the unit can be used. While all static units are different, their purpose remains the same: their activation will help or ease pressure off the lower level player.

Unlike regular operations, M.C. operations have a time limit; if the time runs out, the operation will end in a failure for both players. In addition, both players also share the same Life Point count; if the LP reaches 0, the operation will end in failure for both players. However, similar to Contingency Contract, the results of the operation remain the same regardless of LP count: losing Life Points does not result in a de-valued clear.

When an M.C. operation ends, players may add each other as friends in the results screen.

Miscellaneous

• The game speed setting in M.C. operations is set to 1× and cannot be changed in any way. Selecting units, which usually slows down time, does not do so in M.C..
• Pausing the game requires the other player to accept.
• In the event either player is disconnected, the player will be given a limited time window to reconnect into the game, at which the disconnected player will be returned to the M.C. session. Do note that the operation will still proceed as usual during this time window.
• Exiting the game (directly from the device) prevents the player from reconnecting into the previous session. However, their deployed units will remain on the map.
• To prevent destructive behavior, players who disconnect (whether intentionally or accidentally) or repeatedly leave sessions cannot create or join any M.C. sessions for a certain amount of time.
• Due to the multiplayer function, Arknights' minimal system requirements have been increased to at least 2 GB of RAM for both Android and iOS.
• A good internet connection (with a ping of at most ~100ms) is needed for a smooth gameplay experience.

Season

As of March 9, 2021, Multivariate Cooperation consists of a single season:

Season	Release dates
	CN	Global	TW
#1 (Defence Protocols)	2021/3/9	2021/8/18	2021/9/9