There are four enemies implemented in .kkrieger. While it is possible to complete the game by running past them, they will attempt to block your progress. You are not required to kill any enemies, but they can physically obstruct your movement.
The basic enemy is a small, four-legged walker. It takes two shots from the first two guns to destroy. The third, fourth, and fifth guns kill them in a single shot.
While weak individually, they normally appear in large groups and will converge on your position. However, there is not much worry about them trying to outflank you. They usually appear in a weak echelon formation, which allows clearing them out one-at-a-time or by running past them.
The second enemy that you run into is also a four-legged walker with a spider-like appearance. It has much more health and the ability to fire back at you. Simply strafe to avoid the projectile, and hose it down with your own attacks to kill it.
It is defeated with two or three shots from the first launcher.
This enemy isn't too common, but it may appear in groups.
The third enemy that you find will be the biggest. It's a slow moving robot-like enemy identified by its size and glowing red eyes. Like the medium walker, it can also shoot at you. Keep your distance or you'll take significant damage quickly.
You only need to deal with one of these opponents at a given time, and there is usually no attack wave directly behind them. Any further enemies are located in the next room.
The final enemy that you find won't be so special, but the sight of it might shock you the first time it appears. It runs on the ground like a dog, but has a large, fiery face with curved horns. It takes about 9-10 hits with the third gun to destroy it (about 20 of the normal strikes). Thankfully, it only has a melee attack.
These enemies appear later in the game, and are within the group of smaller opponents.