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 level of the Subspace Emissary stops advancing forwards and locks in place, forcing the player to take on a group of Subspace Army members. Ambushes can be identified by a purple screen flash and a distinctive sound, followed by a series of enemies appearing on a typically designed part of the level. Once all of the enemies are defeated, the screen flashes white and the player can resume advancing through the level.

All levels of the Subspace Emissary contain at least one ambush. They likely exist in order to keep players from simply running through every level without engaging any enemies.

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 bar on the screen showing how many more enemies remain. The Canyon is the only level to be nothing but an ambush.

Trivia

• 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.