The route:
- Get Body Slam
- Can do everything after Slowpokes in red bar (~80% RS range on Gyarados)
- Possible candy to L35
- Can do Celadon Center early to survive Gyarados
- Get Rock Slide
- Do early Koga? Then you can OHKO Silph Gyarados with crit RS and save several turns in setup/healing

Lance:
- Get L55 and near-perfect HP and Special
- Hydro Pump barely doesn't kill after an X Special
- Stall for a miss, then 2HKO with Rock Slide (badge boost essentially guarantees) 
- Use 2 X Attacks (and maybe an X Acc)
- Full Restore as necessary
- 2HKO the Dragonite (Hyper Beam and Agility can be risky)