Stalker (NOTD)

Stalkers are among the most common enemies in game. They make up a large portion of the ambient spawns in all campaigns, particularly Easy Company. Individual Stalkers are easily dispatched, but groups can be difficult to deal with. They are the all-rounder of the infested. They have moderate speed, armor, and health. The ability to climb cliffs, high damage, and moderate stats make them a serious problem in large numbers. Stalkers occasionally spawn patches of creep when they die, greatly increasing the speed of infested hordes. Most weapons fair well against Stalkers.

Cliff Walk
The Stalker has adapted to be able to walk up and down single cliffs. This means that they are capable of negating most of the terrain advantage that a marine has (exceptions include the high walls of the fort) and ambushing players from high ground. This makes them dangerous for unsuspecting players.