Darius is a fast-paced Tower Defense game with a strong card game influence. The game also contains puzzle and reflex elements inherent to most tower defense games. The enemy's main objective is to get inside the player's castle. The player builds different kinds of towers to destroy the enemies and to protect the castle. The enemies will appear in large quantities (called "waves") and the player wins by defeating all waves successfully.
In Darius the primary resource comes in the form of playing cards. Towers are build by playing different cards from the hand. These cards are drawn from the player's decks. The player can draw more cards from the deck using Greenballs, which the player earns by killing enemies.
Darius is a single player game.
The player can select a map from the game menu. Each map consists of several rounds. The player wins by surviving through all of the rounds. Each of the rounds consists of one or more "waves" of enemies which rush towards the player's castle.
Enemies appear on the map in waves. There's a fixed delay (timer) between the waves but the player can skip this and force a new wave to appear instantly. Thus there can be multiple waves in the map simultaneously if the player so chooses.
The player primarily uses towers to defend the castle. Towers can be created by playing different combinations of cards from the hand; specifically a material and a weapon card must be played. The player can choose the place for the tower by pointing and clicking a location on the map. Towers can be placed freely (no prescribed locations) and they will appear instantly (no building time).
Towers are created by playing two different types of cards: Materials and weapons. One card from both types is required for a new tower. The material and weapon selected naturally affect the properties of the tower: Shooting range, damage, shooting speed, the tower's health, etc.
Towers have an infinite amount of ammunition. The towers will get a depleting ammunition reserve if our schedule permits. In that case there will, of course, also be a way to restock the ammunition (the type of ammunition used will depend on the weapon type of the tower).
The monster's sole goal is to reach and destroy the player's castle. They will take the shortest path to this goal. Thus there aren't any preset paths for the enemies to follow, so the enemies can move freely on the map. Some of the monsters are capable of attaking the player's towers as they pass. When monsters are destroyed, the player gets more Greenballs.
The player's card pool contains all the cards the player can use to build his/her decks before the beginning of a map. The player gets more cards to the card pool as a reward for finishing a map. Finishing higher leveled and more difficult maps lead to better rewards.
The card pool will not be reset at the end of the game. Instead the player's collected cards will be saved and can be used again in the next game.
All cards available during a level reside in the player's decks. The player can edit these decks from the main menu. The player chooses the deck contents from their card pool. Decks can be freely assembled but they will have a minimum size. No modifications to the decks are allowed during a level. The player can actually save more than two decks, but is limited to two decks in play.
The reason for a two deck system is mainly strategic. By allowing two different decks in play the player can use one for material cards and the other for other cards, or one deck can be for easy waves and the other for more difficult waves. This system makes this kind of strategic planning possible.
The player will receive an initial amount of Greenballs at the beginning of the level. The player can then use these to draw their first cards.
Even if a player runs out of cards and does not have enough resources to draw more cards the player will not lose the game. Instead, the only (play) option in these circumstances is to wait for the existing towers to destroy enemies, thereby giving the player more Greenballs with which to draw more cards.