I would suggest unlocking 'Gravity Goat' Achievement to unlock the Anti-Gravity Goat mutator first.
Once you have that head over to the slides next to Whiplash on the the Goat Z - Before Oubreak map. Get on the smallest slide and start to slide down. Press
to go limp and once in the air press
to activate Anti-Gravity Goat.
Aim for the small paddling pool pass the big swimming pool, once positioned over the top, press
to deactivate the Anti-Gravity Goat mutator. You should land in it and the achievement unlocks.
At this moment in time it only works on the xbox 360 as its glitched on the xbox one.