tl;dr Pekora bought a
fucking monkey used copy of Pokemon Emerald that was probably hacked with a key item to a nearly 20 year old event you had to physically show up for to capture Mew. She played the event and shiny hunted a Mew. Bowlcuts and Pokemon autists are pissed because you're not allowed to just buy a used copy of a Pokemon game to play an event that is 20 years old and long past any sort of legitimate distribution that is baked into the cartridge.
edit: Reading through MTL of the site it sounds like Cover bent the knee to the autists.