You win a game of Nexus by dealing damage to your opponent while their Life is at 0.

Each player constructs a main deck of cards made up of Attackers, Incantations and Traps alongside a Colour deck. Additionally, both players must have an Avatar card.

Each player starts the game by shuffling their main deck and their Colour deck, alongside placing their Avatar card at the center of their board with their Level 0 form face-up. The player must also take the seven top-most cards of their main deck and place them face-down in front of them: These cards will be a player's Life, and are called Life Cards. After this is done, both players draw five cards.

When a player's Life is reduced, they add a number of Life Cards to their hand equal to the amount their Life was reduced by. If a player takes an attack that would reduce their Life by more cards than they have left, they add all remaining cards to their hand. If a player's life is reduced while they have no Life Cards, that player loses the game.

Players have six primary colours of cards to choose from: Red, Blue, Green, Yellow, White and Black. Each colour broadly focuses on a different type of strategy.

At the start of each player's turn, they will draw a card. A player can have up to 10 cards in their hand, if any cards are added after this point they must discard them to the Trash.

Once per turn a player can pick up the top card of their Colour deck and place it face-up on the field. They may then use whatever Colour card they have drawn to play other cards. When a colour card is used on a turn, it becomes exhausted and can no longer be used. At the start of a player's turn, exhausted colour cards are refreshed and able to be used again.

Players may use these colours to play Attackers, use Incantations, activate Traps or Evolve their Avatar.

Attackers:
Players may control up to three attackers at any given time. Attackers have four different levels: 0, 1, 2 and 3. Higher level attackers require more colour to be played. Excluding the very first turn of the game, an Attacker is able to launch an attack on the opponent as soon as they are placed onto the field. If an Attacker attacks, it is exhausted and can no longer be used until it is refreshed at the start of your next turn. The opponent may use any non-exhausted Attacker to block an attack from an incoming Attacker. If an attacker does not block an attack, your opponent's Life is reduced by the level of the attacker + 1.

If an Attacker does block another attacker, the lowest level Attacker of the two is sent to the Trash. If both attackers are of equal level, both are sent to the Trash.

Incantations:
Incantations may be played during your turn by paying an amount of colour and then sending them to the Trash. They contain immediate effects that are put into effect as soon as the card is played. Some incantations may be played on the opponent's turn, in which case it will say so on the card itself.

Traps:
Each player may set a single Trap card on their field. Trap cards can only be activated when a certain condition written on the card is met. Some Trap cards may require additional colour to be played. Trap cards can be activated on either player's turn.

Avatars:
An Avatar card is the core of a player's deck. They are always on the board and cannot be removed. Avatars have a level 0 and a level 3 side. Players start the game by placing their Avatar with their level 0 side face-up. When the player meets the condition written on the Avatar card, they may flip their Avatar so its level 3 side is now face-up. Level 3 avatars have more powerful effects compared to their level 0 form. This is called "Evolving" your Avatar.

Costs of an avatar can range anywhere from paying a certain amount of colour, removing a number of cards from the Trash from play, discarding a number of cards or any other combination of conditions written on the card.