In the described scenario of a roller coaster moving from point X to point Y, the correct description of energy transformation would be:
Potential energy transfers to kinetic energy, then some kinetic energy transfers to thermal energy.
This is because as the roller coaster moves downwards (from a higher point to a lower point), potential energy is converted into kinetic energy, resulting in increased speed. At the same time, due to friction and air resistance, some of that kinetic energy may also be transformed into thermal energy.