Boss Battle

Everything About Fiction You Never Wanted to Know.
"Mr. Mario, I feel that you and I are destined to do battle, again and again, for so long as the gods see fit."

"Finally! A boss fight!"

Gene, God Hand

A climactic confrontation with a unique, stronger than average, and often monstrous enemy creature known colloquially as a "boss". It has several important features, depending on the genre of game in which it is found.

In old-school Shoot'Em Ups and 2D Platformers, the boss comes at the end of a level or series of levels (commonly called a "world"). He will often require a special trick to defeat, or have a targetable Weak Spot.

In FPS, 3PS's, and 3D platformers, they divide up the game. They might be common or uncommon, gigantic or small, complex multi-stage affairs or simple exercises in circle strafing while shooting.

In RPGs, they wait at the end of dungeons (though the larger dungeons may have multiple boss fights). They have a mountain of Hit Points. If they're the last one, you'll most likely fight them more than once. Most have a specific weakness.

In a Fighting Game, the boss is simply the last character you fight, in that even when the rest of the battles have you going up against a randomly-selected opponent, the boss is always the same. The boss is typically not a playable character (though circumstances may allow him to be unlocked later), and tends to be the most difficult opponent. Occasionally, the penultimate battle will also be against a "boss". (The penultimate opponent is often dubbed a "Mini Boss".)

Note that in some games, the boss isn't always at the end of any given level or dungeon. Also, despite the name, the boss is not always the leader of the bad guys plot-wise, but often is.

Common Boss Battle Tropes