In XCOM 2 Collection, the player-character is the commander of the eponymous military organization that is now reduced to a resistance force opposing the ongoing alien occupation of Earth. The game is played from a top-down perspective and is a turn-based tactics title in which players issue commands to a squad of human soldiers to eliminate the aliens in a map and dependent on missions, complete secondary objectives. Many of the missions are timed, requiring players to complete it within several turns. Maps are procedurally generated to create a wide variety of levels. Every map features different terrain and buildings in each playthrough. The game offers four difficulty settings: Rookie, Veteran, Commander and Legend.
After players complete the campaign, they can start a new game with the "Ironman" mode enabled. In this mode, the player's save file is overwritten whenever the player performs an action, making it impossible for players to import an earlier save after making a poor decision. The game also features a one-on-one multiplayer mode in which players received a fixed number of points to build a squad composed of both ADVENT and XCOM forces, and attempt to eliminate the opponent's squad on a battlefield.
At the start of most missions, the player's squad is concealed and will not be detected by enemies. Players can position their troops to plan their battle and ambush enemies. Fog of war hides the aliens and their actions from view until the player's soldiers are in range and have line of sight on them. Squad members can hide behind environmental objects to avoid being shot. Enemies programmed by artificial intelligence will attempt to flank and exposed soldiers will sustain heavy injuries from hostile attacks due to the lack of any defense. Each turn, players can attack their selected targets with firearms. The game will inform the players of the possibility of landing a successful shot and the amount of health the enemy will deplete. They can also reload, remain in overwatch to shoot any moving enemy in their line of sight, hunker down, and hack into enemies' mechanical weapons like turrets and temporarily shut them down or control them for themselves. Each squad member can perform a limited number of actions before the enemy takes their turn and players can choose to end their turn early.
The game has five character classes, each with its own Soldier Ability; Ranger wields a melee weapon that slashes enemies, Grenadier has a grenade launcher and explosives that can destroy enemy cover, Specialist has a drone that improves the team's defense and health, Sharpshooter is the team's sniper, and Psi Operative—which is unlocked late in the game— uses telepathic and psionic powers. Enemies from the first game in the series, including the Sectoids, returned while Firaxis introduced new enemies including the Vipers, a snake-like enemy who can drag soldiers out of their cover. When a soldier is injured or about to bleed out, medkits can be used to stabilize his or her condition. Soldiers in the squad can be permanently killed by enemies and their bodies can be carried back to extract their equipment should the player deem it necessary to abort the mission. If it is deemed necessary to abandon the mission, a soldier can carry wounded soldiers to extraction where they are revived upon leaving the map. If the soldiers survive and complete the mission, they gain experience and will be promoted, unlocking new options in the skill trees and customization items.