Why can't I use my Gyarados in Pokemon Stadium?
Using a Pokemon Blue cartridge.
Trying to play 25-30 league, my other pokemon in that level range show up but no Gyarados. He's level 28.
Does Gyarados not exist in Stadium?
Solution 1:
According to the Wikipedia article on Pokemon Stadium , the Petit cup is more restrictive than just level:
Petit Cup: Battle using Basic Pokémon from levels 25 to 30 who fall under a certain height and weight. The most restrictive Cup.
Not only that, but it turns out you can't even use evolved pokemon. Gyrados breaks more than one rule. I think you'll find many of your pokemon aren't selectable for this event.
The rules for the Petit Cup can be seen here on IGN:
Blue Panels (Qualifying Pokemon): 45 Description: Press A when you highlight this rule, and it will bring up a list of Pokemon. Pokemon in blue boxes can be used but ones in red boxes cannot.
Enter with six Pokemon. Description: Choose six Pokemon before going to battle. You may not choose more than one of a certain kind of Pokemon.
Choose three out of six Pokemon. Description: Out of the six Pokemon chosen, choose the three that are to be used in battle. Try to choose the three battle Pokemon that have advantages over the likely opponents.
Levels 25 to 30. Description: Pokemon of levels 25 to 30 may be used. If you don't have six Pokemon, you may add Rental Pokemon.
Maximum three-Pokemon level total 80 Description: The combined levels of the three battle Pokemon may not exceed 80.
Max. HT 6' 8'' and max. WT 44 lbs. Description: The height of Pokemon may not exceed 6' 8''. Likewise, the maximum allowable weight is 44 lbs.
Un-evolved Pokemon only. Description: Only un-evolved Pokemon may be used.
No two Pokemon asleep or frozen. Description: If one Pokemon falls asleep, none of the others can be put to sleep by an opponent. The same goes for freezing. It is possible to have one Pokemon asleep and another frozen.
Mew can't attend. Description: Mew may be used only for the Gym Leader Castle, Prime Cup, and Free Battle.
Get a continue for a perfect match. Description: You earn a continue for every battle won without a fainted Pokemon. If you have a continue, you may try again after losing a battle.
No Selfdestruct move with last Pokemon. Description: If your last remaining Pokemon uses Selfdestruct or Explosion, you lose, even if the opponent's last Pokemon faints.