The game "First Encounters with Aliens" takes place in modern-day American suburbs, where alien objects have appeared and given people the ability to see alien memories encoded in Engrams. The player must build an outpost and race to summon a powerful entity in the preparation phase. The player who summoned the entity takes control in the arrival phase and uses its abilities while others attempt to commune or destroy it. The game consists of 60 location cards, 40 engrams cards, and 20 arrival cards, as well as 5 hero, HQ, entity, and boon cards.

The game has several card types: "Locations" represent buildings and spaces, "HQ" locations are special spaces each player starts with, "Engrams" are permanent status effects that increase power and affinity with entities, "Arrival Actions" are abilities executed by a controlled entity during the arrival phase, "Heroes" have innate abilities and stats held by their player, "Entities" have innate abilities and stats and are used to keep track of abilities and health when controlled by a player, and "Boons" are special cards with various effects awarded for making peace with entities.

The game has an in-game resource called "Stacks," which is a limited resource that can be saved between turns to spend on abilities and upgrading locations.

During the Prep phase, players can play 1 Location per turn to gain abilities and resources, unless a card allows more. Locations are played in Clusters and provide either Energy (denoted by a blue diamond) or Stacks (denoted by a gold coin). Clusters have an Energy Level equal to the number of Energy-providing Locations. Locations track damage against their Toughness value. When damage exceeds a location's Toughness, it is destroyed. Locations have various properties, abilities, and requirements, like the Energy Level required to play the Location. Locations cannot be played in the Arrival phase.

Each player has a "Hero" represented by a figurine on the game board, with attributes and abilities on a card in the Hero Zone. Heroes occupy and move between clusters, able to move once per turn unless a card allows more. During the Prep phase, heroes remain at their HQ and can play abilities from any locations within their territory. During the Arrival phase, heroes can move to any cluster but can only activate abilities at their current cluster. When damage is dealt to a cluster, any heroes at that cluster take damage as well. Hero cards have properties such as Name, Starting Health, Attack Damage, Hero Ability, Ultimate Ability, and Unique Win Condition.

The 5 entities, in order from least to most powerful are: The Althumans (similar in power to a human), The Glitchkin, The Quantites, The Thoughtflame, and The Silver Beasts (almost godlike power).

Althumans are from an Extradimensional Earth that is similar to ours but more technologically advanced, with mostly desolate and overgrown areas and a small number high-civilization cities.

The Glitchkin are an AI collective from an Extradimensional Earth that suffered an AGI singularity and began probing another Extradimensional Earth with drones. This led to the discovery of advanced technology and extradimensional travel by the Althumans.

The Quantites are a trio of entities with high perception and a unique matter signature that allows them to exist and not exist in spaces, resulting in ghostly appearance and ability to phase through matter. They have encountered Glitchkin drones and suffered losses to Silver Beasts. Some speculate about "Quantum Mirror Reverberation Shatter.”

The Thoughtflame gained the ability to concentrate their consciousness in hot aetherflame, transforming their bodies permanently into stonelike shards coursing with flame. They lost their home world to the Silver Beasts' quest for silver fuel; many ascended into flame to survive the Silver Beasts' attack.

Silver beasts are colossal silver-reflective beasts - dragonlike, with horns, mammalian features, rhinolike armor, all mirrored and reflective. they are hundreds of feet tall typically but shrink their stature when the situation wants it. they are on an unrelenting quest for silver to build a new godlike silver beast.

Entities can be summoned to the game board by players at monolith locations with varying affinity requirements from 1-5. When summoned, the Arrival phase begins and entities have properties such as Name, Health, Harmony, Attack Damage, Minor Ability, Major Ability, Harmony Ability, and Win Condition.

When an entity is summoned, the summoning player draws X cards from the arrival deck based on their affinity for that entity. They play as the entity after their own turn, using arrival cards instead of hand cards, until they run out of cards to play. Entities move on the board, play arrival cards, and use abilities, including a basic attack by discarding an arrival card. Heroes can attack entities or attempt to make peace with them, if they are in the same cluster.

Making peace with entities is a hero ability that requires a die roll plus affinity to exceed the entity's "Make Peace" difficulty. The die and difficulty vary by entity. Success results in the entity being removed from the board, the arrival phase ending, and the player earning the entity's Boon - a card with a unique effect. Boon cards have properties such as Name and Ability.

Defeating an entity in combat by reducing its health to 0 will end the arrival phase, remove the entity from the board, and reward the player with a large amount of Stacks. Defeated entities can no longer be summoned.

In the game, each hero has a specific win condition, such as defeating two entities on their territory, making peace with two entities, collecting $100 and upgrading their HQ, or gaining an affinity of +10 for a single entity and then summoning it. Additionally, there is a generic win condition available to all players, which is to have the last HQ standing in the game. The number of entities included in the game can be adjusted to change the length of the game, with players able to choose from 1 to 5 entities before the game begins.

Each player starts the game with one of the five special locations called "HQ's". The HQ has a defensive ability and can be upgraded. The upgraded version of the HQ is associated with one of the five entities, and grants Engrams for that entity upon upgrading.