Parallel drainage pattern. A parallel drainage system is a pattern of rivers caused by steep slopes with some relief. Because of the steep slopes, the streams are swift and straight, with very few tributaries, and all flow in the same direction.
1 In Creative, the player can use spawn eggs to spawn most mobs. 2  When mobs are spawned this way, all normal spawning requirements, such as light level and block type, are ignored. 3  Any entity can be spawned using the /summon command.
Mobs will spawn only when you want them to. If you're really committed to the idea of doing this with /kill, however, you can do this one of two ways. You can set up individual command blocks to kill each type of mob, which might be a small set of command blocks if your main problem is slimes.