Along with Time Units, a unit's Reaction rating is one of the most vital resources a unit can have in combat. Reaction influences precedence - who gets priority to make their move. It is used offensively and defensively. The side that's currently issuing orders (the attacker) uses reactions to prevent opportunity shots while the waiting side (the defender) uses reactions to take shots of opportunity.
When two opposing units are within range of each other, the Reaction levels of both units are compared. The unit with the highest Reactions gets to make the move. If the defender is not aware of the attacker, no check is made. However, as soon as the defender is made aware of the attacker, a check is made and will then perform an attack of opportunity if the conditions for a reaction shot are satisfied. Note that if an attacker with lower reactions is exposed to a defender with high reaction due to the actions of another unit (such as shooting away a wall), the check is not made and the exposed attacker is not fired upon. However, the moment the exposed attacker moves, the defender will be able to obtain an attack of opportunity given the right conditions.
What is not common knowledge is how the overall reaction level of any given unit is also influenced by the percentage of the unit's remaining TUs! So say an alien has 100 reactions but only has 60% of its remaining TUs. Its actual Reaction level is really 60, not 100. If it takes a Snap Shot, which costs 30% for any plasma weapon, the remaining TU percentage will drop to 30%, and so will the Reaction level. For more information, see Reaction fire formula. --JellyfishGreen 10:51, 25 Apr 2005 (BST)
With this in mind, one could say that for the best opportunity attacks, end your turn with full TUs, wielding weapons with low snapshot costs. The Pistol, Laser Pistol, and Laser Rifle are by far the best weapons in the X-COM arsenal for attacks of opportunity. Still, these weapons (especially the standard pistol) may not be enough to take down e.g. Mutons. Adapt to your situation.
For melee attacks, it is often best to use a mind probe to examine the stats of any alien that you wish to approach. By getting an overall impression of the alien's remaining TUs and its reaction level, you can get a good idea of how safe the alien will be to approach.
New recruits will always begin with a value between 30 and 60.
Reaction points are awarded (at end of combat) depending on how many times you took reaction shots. Missed reaction shots do count - all that matters is that you reacted. (Misses don't count for Firing Accuracy increases, though.)
You can be awarded up to an average of 4 skill points (range 2-6) per combat mission if you make at least 11 reaction shots. The point award does not depend on your current skill level, only on the number of reactions. For more particulars on skill-point increases, see Experience.
Note: Although there are several area-effect weapons that can be fired with a reaction shot (stun bomb, auto and heavy cannon, rocket launcher), each reaction shot only gives you 1 point of reaction experience, even if the shot impacts numerous aliens. From the game's perspective, you were only reacting versus one particular alien. However, multiple hits from one reaction shot will give you multiple experience points toward firing accuracy skill increase.
An X-COM soldier's Reactions are capped at 100. However, because you can get a +6 roll when at 99, a soldier can have up to 105 Reactions (if they're really lucky!). For more info, see Regarding Caps.
- Reaction fire formula
- Reaction fire triggers
- Advanced skill increase techniques:
|X-Com: Enemy Unknown/UFO Defense|
|Soldiers:||Time Units • Energy (Stamina) • Health • Bravery • Reactions • Firing Accuracy • Throwing Accuracy|
|Strength • Psionic Strength • Psionic Skill • Melee Accuracy • Stun • Morale • Rank • Fatal Wounds|