>>13569371Reptiles need the heat from the sun in order to survive, this we know, but because they lack a way of regulating their body temperature, they also very easily overheat if they sit in the sun for too long, that's why they have a cycle finding shade and then basking again, sun to shade, to sun, to shade etc.
Helioptile is a reptile, hence why he needs the sun, but is also harmed by it, if it is intense.
Screencap to educate.