Introduction: Minecraft PE: Mob Rollarcoaster
Make a roller coaster track (any track works, and be sure to add powerails)
Place a Minecraft on the track. Don't hop in it! Just walk into it and it should start going around the track on its own.
Once the Minecraft is going around the track spawn any mob (evan endermen) on the track.
The cart should pick up the mob as it moves round the track.
Now you have a mob rollar coaster