XII Stag is a vertical scrolling arcade shooter. The player controls a futuristic aircraft and tries to reach the end of each stage, where a boss fight waits. There are several different types of attacks: a regular shot, which can be upgraded five times by power-ups dropped by enemy ships; a side attack is a risky manoeuvre that involves pushing the control stick quickly left and right to destroy enemies to the left or right of the player's ship. This will also increase the score multiplier. The ship's exhaust can also be put to use by damaging enemies that come up from behind. The final weapon is the barrier, which creates a protective ring around the player, destroying all enemies that touch it. The game also features a difficulty setting adjusted dynamically by the score - the higher the player scores, the more difficult the game gets. XII Stag also has checkpoints in each level, which compare the current player's score to the high score at this point in the game.