As Toby descends the half-pipe, there is a transformation of energy from gravitational potential energy to kinetic energy.
Initially, when Toby is at the top of the half-pipe, he possesses gravitational potential energy due to his height above the bottom of the half-pipe. As he starts to descend, this potential energy is converted into kinetic energy as his speed increases.
In summary, the energy transformation occurring is:
Gravitational Potential Energy → Kinetic Energy.
This transformation continues until he reaches the bottom of the half-pipe, where most of the gravitational potential energy will have been converted into kinetic energy, assuming negligible losses due to friction or air resistance.