Many single-player games feature a level/episode structure, the game becoming progressively harder as the player advances. Bosses are a consequence of this structure, appearing at the end of a level or episode, and being the hardest enemies to defeat. Others have a storyline and no level-based structure, but still feature boss-like enemies at various points in the story or at the end of the storyline.

Games make bosses difficult to kill by giving them more hit points (amount of damage they can sustain) and more effective attacks. In complex games (particularly role-playing games), bosses also have "special" attacks, such as stunning/freezing the player, teleportation, inflicting curses on the characters that decrease their abilities, and so forth. Bosses are often immune to certain abilities that the player possesses, and often can only be defeated by specific attacks, or by using the environment or their own attacks against them.

A weaker version of a boss that appears earlier in the game is called a miniboss.