For terrain challenges see Concept:Obstacle.
Enemies are made to defeat you, usually by beating you at a game or killing you. They are an important aspect in nearly all levels/worlds.
The "Killing" Aspect
Enemies are mainly made to kill opponents, usually due to easier building and more theme. They are usually made using tags and/or lasers, although some may indirectly kill you.
In combat worlds using blocksters as avatars, blocksters or Leg Piece are commonly used to create combat enemies. They are usually given tags, which will then kill the main player. Sometimes the blocksters themselves are given lasers and forced to face the player, allowing a more interesting world. When blocksters are trapped within walls or simply out of control, sight line and wait icons can become usefull.
Laser enemies shoot out of walls or vehicles, sometimes facing the player and sometimes locked in different directions. Though they usually kill, they can be used to weaken the player or set off traps.
The most common way to have an enemy indirectly kill the player is through shoving off edges. This is usually done through wheels and other Action Blocks.
Sometimes levels are made where the level is an arena with multiple "sumo" enemies attempting to shove you into lasers or off the edge, but you must kill them first. These levels are fast and fun, and usually get lots of likes.
The Competition Aspect
It may have been brought up earlier, but sumo fights are regular competition
Sometimes races with CPU challengers are done. Unfortunately, these are difficult to program and tend to be very glitch and laggy.
Races are sometimes done with multiple characters, it this causes even more difficult programming, as well as more glitches and lags