I'm currently thinking about grinding up some Pokemon at the Elite Four in a nuzlocke (I have 14 badges). However, I'm curious to know if Silver challenges you with only 6 of the Kanto badges or if he challenges you with all the badges.
On Mondays & Wednesdays however, when you enter the Pokémon League, you will get challenged by your rival before you enter. He has been training and wants to test his team out
Source
You’ll be able to initiate rematches with your rival at the Pokémon League just by completing a short post-game side-quest.
The side-quest involves two main things:
You’ll need to defeat your Rival in Mt. Moon in Kanto Then you’ll need to team up with your Rival in a double battle in the Dragon’s Den, located behind the Blackthorn City Gym
After battling Silver at Mt. Moon, and then flying to the Dragon's Den and battling with him there, Silver is able to be battled at the Pokemon League on Mondays and Wednesdays.
Hope I helped!
