This is an amazing creation that allows you to create many different mobs!

So far it uses 3 command blocks, one for fun that creates a title on the screen, one for the main spawner, and one for the following aspect. 
Go ahead and see what you can make! 

Either continuously flip the lever, or replace the redstone in the clock in the center command block to spawn whatever you want.
If you want to change what spawns, right click the command block and replace /summon "Minecart" with /summon "Whatever Entity You Want"

If you have any questions, ideas, or just feedback then comment below!
It is very simple to operate and keep in mind that I will continue adding to it!