This is a
skateboarding trick which is a mixture of the
hardflip and
impossible. Hence, it is best to learn both these tricks before attempting it (it is however easier than an
impossible, so you may simply want to learn the
hardflip.
This can be done stationary, though it is considerably easier down at a medium-slow speed. Ollie, getting a bit of height, and push down with your back foot as if doing an impossible, but at the same time heelflip or kickflip with your back foot (often easier to heelflip). You only want it to do half a heel/kickflip, so don't kick it hard. As it comes up (beggining to show its underside) it should be heel/kickflipping, and once it comes down the other side it should have the griptape showing up, instead of the underside. Catch it and ride off, the trick is easier than it sounds.