Ambush

An ambush in The Research Facility I. Note the typical "ambush design" of the place battled in, and the slight dark fade.

The Canyon, a level only consisting solely of an ambush with an enemy counter.

An ambush or a locked battle is when a side-scrolling level stops having the player continue forward and locks in place, forcing the player to take on a group of enemies. Once all of the enemies are defeated, the player can resume advancing through the level. They likely exist in order to keep players from simply running through every level without engaging any enemies.

Ambushes in Melee's Adventure Mode are not common and shown simply by the camera focusing on a specifc part of the stage instead of following the player. Ambushes in Brawl's Subspace Emissary can be identified by a purple screen flash and a distinctive sound, followed by a series of enemies appearing on a specially-designed part of the level; when an ambush is over the screen flashes white with another distinctive sound. All levels of the Subspace Emissary contain at least one ambush.

Certain levels - namely Midair Stadium, The Battlefield Fortress, The Canyon, Outside the Ancient Ruins, and The Subspace Bomb Factory II - have situations similar to ambushes except for the fact that the battle takes up an entire piece of the level, instead of being a blockade in the middle of a level. These ambushes generally have a higher enemy count, alongside an extra display on the screen showing how many more enemies remain. The Canyon is the only level to be nothing but an ambush.

Trivia

• Unlike other ambushes, fights with Link in the Underground Maze are not initiated until the player is grounded. This makes it rather trivial to simply jump through potential ambush rooms to avoid fights.
• For most ambushes, parts of terrain that aren't connected to the main area and are just off-screen become disabled, preventing players from being rescued by a bounce off of an unseen object.
• Glires, Glices, and Glunders tend to take themselves out of ambushes, due to rolling along terrain that leaves the screen.
• Humorously, there is a locked battle in Subspace (Part I) that contains nothing but a Ticken - which appears above no platforms and promptly falls off the screen.