A: Look for the "Post-Game" section of the trainer doc. You can rematch gym leaders at the Fighting Dojo in Saffron City. Their teams are level 75-80 and include legendaries.
Furthermore, Johto’s infamous level curve is fixed. The level jump from Jasmine to Clair is smoothed out, but the power jump is immense. Without documentation, you will walk into Clair’s Kingdra only to discover it has Draco Meteor and a Lum Berry . pokemon sacred gold storm silver documentation top
Bugsy’s Scyther (Level 17) has U-turn and Technician . Solution via Doc: Route 35 (night) has Geodude (High Defense) or Magnemite (Steel typing). A: Look for the "Post-Game" section of the trainer doc
Good luck, champion.