Take the Goldenrod Center, get Return, then bike to the Radio Tower.
 
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IF EARLY UNDERGROUND:
 
RADIO TOWER 1
- ROCKET 1: Strength x2
- ROCKET 2: Surf
- ROCKET 3: Strength x2
- ROCKET 4: Strength x2, Strength+IP
- ROCKET 5: Surf, Strength, (swap Bite), Bite x2
- SCIENTIST 1: Surf x3
- SCIENTIST 2: Surf+Bite
- EXECUTIVE: Surf x3, Bite+Surf, Surf x2
 
(Get Return and Calciums)
(Use Calciums, use Ether on Surf, and teach Return over Bite)

UNDERGROUND
- RIVAL 4: X Spec, Surf x2, IP x2, Surf
- ROCKET 1: Return
- ROCKET 2: Return x3
- ROCKET 3: Return x2
- BURGLAR 1: Return x2
- BURGLAR 2: Strength x3
- ROCKET 4: Strength x2
- ROCKET 5: Surf x2
- ROCKET 6: Surf x2
- ROCKET 7: Surf x2

RADIO TOWER 2
- ROCKET: Return x2
- EXECUTIVE 1: IP+Surf
- EXECUTIVE 2: Surf, IP, Return
- EXECUTIVE 3: Return, Surf x2

BLACKTHORN GYM
- COOLTRAINER 1: Return x2, Strength       
- COOLTRAINER 2: Return x2            
- COOLTRAINER 3: Strength x3
- COOLTRAINER 4: Strength, IP          
- CLAIR: IP x3, Return x2       
 
DRAGON'S DEN
- COOLTRAINER: IP

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IF LATE UNDERGROUND:

RADIO TOWER 1
- ROCKET 1: Strength x2
- ROCKET 2: Surf
- ROCKET 3: Strength x2
- ROCKET 4: Strength x2, Strength+IP
- ROCKET 5: Surf, Strength, (swap Bite), Bite x2
- SCIENTIST 1: Surf x3
- SCIENTIST 2: Surf+Bite
- EXECUTIVE: Surf x3, Bite+Surf, Surf x2
 
(Get Return and Calciums)
(Use Calciums, use Ether on Surf, and teach Return over Bite)

UNDERGROUND
- DONALD: Return x2
- TERU: Surf x4
- RIVAL 4: X Spec, Surf x2, IP x2, Surf
- ROCKET 1: Return
- ROCKET 2: Return x3
- ROCKET 3: Return x2
- BURGLAR 1: Return x2
- BURGLAR 2: Strength x3
- ROCKET 4: Strength x2
- ROCKET 5: Strength x2
- ROCKET 6: Surf x2
- ROCKET 7: Strength x2

RADIO TOWER 2
- ROCKET: Strength x2
- EXECUTIVE 1: IP+Surf
- EXECUTIVE 2: Surf, IP, Return
- EXECUTIVE 3: Return, Surf x2

BLACKTHORN GYM
- COOLTRAINER 1: Return x2, Strength       
- COOLTRAINER 2: Return x2            
- COOLTRAINER 3: Strength x3
- COOLTRAINER 4: Strength, IP          
- CLAIR: IP x3, Return x2       
 
DRAGON'S DEN
- COOLTRAINER: IP