Suppression is an ability of the Heavy Class, Thin Men, Heavy Floaters, Mutons, and Muton Elites in XCOM: Enemy Unknown. S.H.I.V.s of all types can also gain this ability with the S.H.I.V. Suppression upgrade. The Support Class can be trained to use a functionally identical ability, Rifle Suppression.
|“||Fire a barrage that pins down a target, granting reaction fire against it and imposing a 30 penalty to Aim.||”|
– In-Game Description, XCOM: Enemy Unknown
Suppression can be useful for pinning down a target, especially when soldiers are otherwise unlikely to hit or kill it. This can buy time to get soldiers to cover or into position to flank the enemy. Suppression is capable of destroying cover, leaving the enemy exposed to fire (and increased critical hit chances) from the rest of the squad. This promotion is especially useful for neutering Sectopods (or Mechtoids in XCOM: Enemy Within) who can fire twice per turn.
Suppression, like Smoke Grenades and Flashbang Grenades, often encourages enemies to choose alternative forms of attack (grenades, poison, psionics, etc) which are not affected by the Aim penalty; none of these actions trigger the reaction fire from Suppression. Enemies lacking in any effective alternative offensive actions are more suitable targets for Suppression, while the other types should simply be killed. A special exception is the Sectopod, as where its Cluster Bomb secondary attack is very damaging, the delayed nature of its targeting system is more manageable by either evacuating your squad (and/or any friendly units) from the to-be-affected area, or simply destroying it before launch.
Suppression often less effective at preventing enemies from hitting their targets on the higher difficulties as most enemies receive Aim stat increases; instead at least two (or more) suppression-effects are required to reliably disable a target's weapon fire. It is often better to Hunker Down with an alien in sight or to enter Overwatch after a short retreat.
Suppression can be used to negate an enemy's Overwatch which can be a nice secondary option to an Assault with Lightning Reflexes; that said, if multiple aliens go on Overwatch, it may be better just to park the squad and take a free turn's worth of potshots at everything without fear of retaliation.
While Suppression can be used to "lockdown" an exposed target or to prevent an enemy from moving into a flanking position, it can be argued that entering Overwatch is more effective as doing so can potentially lockdown multiple enemies AND deter other foes in cover from moving. Suppression tends to be more effective when there are other factors that might trigger (and thus neutralize) Overwatch such as if melee enemies are present or if there is a chance of another hostile pack joining the fight that turn.
Regardless of the synergies and tactics used with Suppression, players who incorporate heavy use of this ability will find the Ammo Conservation research at the Foundry to be particularly beneficial, as otherwise Overwatch expends 2 rounds of ammunition (out of the normal capacity of 3) in LMG-class weapons. This will end up necessitating a reload almost every other turn. The aforementioned research upgrade doubles the ammo capacity to 6, for which a Suppression-focused Heavy will arguably find the most benefit, compared to any other class build.
Where Suppression shines is how well it synergizes with Heavy class abilities from the right side of the promotion tree. Holo-Targeting + Suppression reduces the enemy's Aim while simultaneously increasing other soldiers' Aim against that target. Danger Zone + Suppression increases the Suppression effect from a single target to a small area, which can result in suppressing multiple targets at once and (potentially) granting reactive fire on any one of the targets. Mayhem + Suppression offers minor, reliable AoE damage with Suppression; this is especially useful for mopping up multiple weakened aliens or getting a small amount of guaranteed damage when a regular shot is unlikely to hit.
- The ammo required just to initiate Suppression is twice that of standard fire; at least a third round will be expended if the target moves, and potentially a fourth if the soldier also has the Rapid Reaction rank perk which allows a secondary reaction shot. This can result in the Heavy starting the next turn with a severely depleted if not completely empty weapon.
- This ability is used by EXALT Heavy and EXALT Elite Heavy units in XCOM: Enemy Within.
Sometimes it's not possible to use Suppression even though a normal shot is available. Even with a target visible and the Fire option available, clicking on Suppression shows the message "No targets within range." The same has been observed with the Support's Rifle Suppression skill. See video for demonstration.