How to build it:
Step 1, place a command block and enter "/summon [Mob] [X] [Y] [Z]" and attack a lever next to it. Enter the xyz coordinates on the place where you want the launcher to be, with precision of 10.
An example of the command block command:
Step 2, build a 1*1 chamber and put glass pane in front of it, then build a long ice path.
[b|Step 3[/b], activate the lever for about 30-60 seconds
Youre done! This is how to use it:
Go in front of the glass pane, and walk towards it.
This is how far it will move you:
If you want to launch mobs, simply spawn the mob under the glass pane.
Want to delete all the mobs in the chamber? Just do "/kill @e[type=Mob]".