i just wanna know if i'll replace one of my magnezone's moves.
No you do not Flash.
As there are no dark caves in Generation VI, Flash will instead cause the screen to zoom out, revealing more of the surrounding area than normally is visible. In addition, it also decreases the chance of encountering wild Pokémon.
The only cave where Flash can be used in Pokémon X and Y is Reflection Cave.
TM70 Flash can be obtained as a gift from Tierno in Reflection Cave.
Source: http://bulbapedia.bulbagarden.net/wiki/Flash_(move)
Hope I helped :)
Playing through the main Story You will not need flash But it will be given to you as a TM Hope I helped Source:experience
