New Mechanics
After beating the game, random weather affects start appearing across the map (cities and routes). Included in these effects is the new shiny fog/mist. This fog/mist increases shiny rates to 1/256 (TBD).
Secret bases are removed and replaced with secret grottos. These can be opened at former secret base locations, and contain rare spawns and a chance at increased shiny rates. When you enter one, there is a 1/4 (TBD) chance for shiny rates to be boosted to 1/256 (TBD) with an audible chime if the shiny rate chance activated. After you leave, the grotto closes for 20 hours.