Reaction Fire
Overview
Reaction Fire or Opportunity Fire is the ability for a unit that is not currently taking its turn to override the other side and make an attack against it. Thus the name opportunity fire.
Reaction Level
A unit's reactions are a measure of the unit's ability to react, but this is only a part of a whole.
Current Reaction Score = (Reactions Stat) × (Current Time Units / Max TUs)
Your unit's actual reaction score, also known as initiative, is the reaction stat multiplied by the percentage of remaining TUs. Here Max TUs refers to the maximum number of TUs that can be regenerated each turn.
As you spend time units on any actions, initiative weakens by a percentage of how many time units were spent for that action against the maximum possible time units.
If for example you have 32 of 64 Time Units and 50 Reactions, you are therefore only able to use 50% of your reaction level, or 25 out of the 50.
Let's say one step is taken, costing 4 TUs.
(32 - 4) / 64 = 0.375.
50 * 0.375 = 18.75.
Rounded down to the nearest integer, you will now only have 18 of 50 reaction to defend against reaction fire.
From this we can see that a soldier who decides to end the turn without spending any time units will often have a much higher initiative level than one that has spent most if not all of the time units. This means the less time units spent, the higher your chance to react.
When and how is it used?
You can think of reactions as having two inherently identical but different roles: defensive and offensive.
Defensive use of reactions occurs during your turn to protect you against reaction fire.
Offensive reactions is the exact opposite, it occurs when you are not taking your turn to perform attacks of opportunities against enemy targets that have a lower initiative.
Visualise every unit on the field as having a place in an action queue based on their initiative level. All units currently making the turn will slowly drop their position in the queue as they spend their time units performing actions.
The side making the move can move any unit at any point in the queue as they please.
As soon as any unit on the waiting side jumps up in the queue above any unit on the moving side it will counter with a reaction shot as long as it meets all the conditions to perform the shot. This action costs time units, therefore instantly dropping the reacting unit's place in the queue.
This whole process keeps going until the end of the turn, and is repeated with the sides swapped. The process starts over again at the start of the next turn.
Using Reactions Defensively
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Tip: Use the Mind Probe to determine if an alien is in fact out of Time Units. This can give you a good indication of whether or not the alien will be able to react should you need to shoot, capture or approach the alien to strike it with the stun rod. |
The side making the current move will use their initiative levels to defend against the waiting side.
During your turn, when your soldiers are given orders that can trigger reaction fire, the unit's current reaction score is directly compared against the current reaction level of any alien that can see the unit. Naturally, if the enemy is looking the other way or there are obstructions, it will not be able to react even if it has the greater reaction level. The same applies if it doesn't have enough time units to perform an attack.
As long as your initiative is higher, you will be able to make any move you wish. The moment the enemy has a higher score, it will be able to interrupt you with an attack of opportunity - or reaction shot - if it has enough remaining time units to shoot.
In this sense, you are using your reactions to defend against enemy opportunity fire.
Note that AI controlled units are allowed to react with auto or snap shots.
Using Reactions Offensively
At the end of your turn, your roles are reversed. Your units will now wait and open fire on any enemy units that are within their line of vision that have failed their initiative.
The waiting side is always on what's known as Overwatch mode, where they will attack the moving side as long as they meet several necessary conditions. This being that the moving side performs an action that brings its unit into visual range of a waiting unit. Also it must perform an act that can trigger reaction fire and the defender must have sufficient time units to perform an attack.
Player controlled units will only react with snap shots.
A Working Example
This short example will follow two opposing units that have spotted each other. For the sake of this example, they will be called Werner Okamoto and Generic Nasty Alien Shaped Thing (GNAST). Both units will have the following stats at the end of the turn.
Werner Okamoto
- Time Units: 60/60
- Reactions: 30
- Weapon: Laser Rifle (Snapshots cost Werner 15 TUs)
GNAST
- Time Units: 25/50
- Reactions: 70
- Weapon: Heavy Plasma (snapshots cost GNAST 20 TUs)
The human turn is ended. The aliens now get to choose what to do. Naturally, since the alien can see the soldier, it will attempt to attack.
This example uses the assumption that the AI will only use snap shots in this exchange, and that both units are unable to kill each other throughout the exchange.
Move 1
Werner = 30 * (60 / 60) = 30 * 1 = 30 GNAST = 70 * (25 / 50) = 70 * 0.5 = 35
The above listed numbers represent the reaction level of each unit during each stage of this exchange. In this move, because the alien has the higher initiative, it takes a shot. This deducts 20TUs and leaves it with 5 TUs.
Move 2
Werner = 30 GNAST = 70 * (5 / 50) = 70 * 0.1 = 7
Not only does the alien not have any time units left for the shot, it has lost the initiative. Werner takes the shot. His TUs at the end of this move is 45.
Move 3
Werner = 30 * (45 / 60) = 30 * 0.75 = 22 GNAST = 7
Werner shoots again, spending 15 more TUs.
Move 4
Werner = 30 * (30 / 60) = 30 * 0.5 = 15 GNAST = 7
Werner shoots again, spending another 15 TUs.
Move 5
Werner = 30 * (15 / 60) = 30 * 0.25 = 7 GNAST = 7
Although equal, Werner can still make his 15TU shot while the alien cannot fire back. Werner takes one last shot. As this exhausts Werner's TUs, the exchange of shots end. The alien is now free to spend the remaining 5 TUs in whatever actions that it fancies.