>>42522527Masuda is a 6/4096 rate of shiny (effectively 1/683) Shiny charm is x2 rolls per encounter on top of any other modifiers (8/4096 = 512)
Code's bugged to fuck, but the intent was there, given they explictily mentioned it on the Pokémon website - w/o charm, 500 battles gives 6 times the chance, or the exact same as Masuda w/o charm.