You have to know how to Indy Grab and 180 before you try this. This is best done of the side of a huge ramp.
I first learned this on a ramp. I went of the side because that's easier. You can do it however you like you just need to have about 2 feet of air. Go really fast because you need big air. Ollie up like a regular 180 off the side of a ramp. Then When your down about 45 degrees Grab and Indy. At first it is hard to grab but just remember when your taking off the ramp tuck your feet up. It took me 2 tries to land so it shouldn't be that hard. Just Ollie and Grab. It's that easy!