Watch on youtube

Download link: http://www.planetminecraft.com/project/ ... minecraft/

My youtube channel: http://www.youtube.come/MegaDerf110

It looks like many people want to know how to make custom mobs spawn naturally, at least I've seen a few topic on the Minecraft Forum where people wanted to know how to do that. So I decided to make a video about it.
The contraption I built is mainly an example and it can be easily modified to spawn any custom mob you want. I have added three custom mobs.
The first two custom mobs are easier to spawn, but the third one requires more command blocks because it needs a summon command instead of an entitydata one. That's because the third mob is actually a skeleton riding a cow, while the other two are not riding other mobs.
The system consist in a timer giving points to each new mob. Then a randomizer activates a command block that tries to modify a mob with a low score, meaning that it was just spawned. With the skeleton that command block doesn't modify the mob, but it tags it so other command blocks can summon the new mob on its position and then kill the old mob.
If you want to know more about this contraption, please watch the video and/or download the world save or the schematic file. Just remember to push the buttons to create the scoreboard objective if it's the first time you run this contraption in your world.

IMPORTANT:
You are allowed to use this particular design in your own projects, but remember to give credit to me and to make it clear that you are not the creator of this design. If you don't know how to give credit, leave a comment here or send me a message and I will answer.