In a frictionless environment, all of the energy an object has due to its height off the ground (gravitational potential energy), will be transferred to its speed at the bottom of the hill (kinetic energy).
Then, all of the kinetic energy it has at the bottom of the hill will be turned into gravitational potential energy as it returns to its original height. This allows it to fall again.
The skater can't gain height without losing speed, and they can't gain speed without losing height.
This is the Law of Conservation of Energy. You can't get something for nothing; you only get out what you put in.
(There's that life lesson again.)
*In other words, as long as there is no friction, if the height of the first hill is larger than anything else, the skateboarder will have enough speed to make it through to the end no matter what design is in the middle.*
Some people think that the shape of the loop matters, but keep in mind that this is a frictionless environment; no energy is lost in tight corners.