I want to know whether I need to use up two move slots for my Empoleon or not. So, I know Waterfall is mandatory, but I want to know if Surf is. This might seem useless, but Surf wasn’t mandatory in Unova, so it might not be in Sinnoh.
Yes, you do need a pokémon to know to complete the main story. I know that there are probably more, but I know you need surf to complete Victory Road.