AttackSummon Storm
Flip 2 coins. If both of them are heads, this attack does 20 damage to each other Pokémon (even your own). Don't apply Weakness and Resistance for this attack.

Gyarados is Pokédex #130, generation 1 (Kanto). Giovanni's Gyarados is a Stage 1 Water Pokémon with 90 HP. The card lists level 40. The card says it evolves from Giovanni's Magikarp. In this catalog that name is Magikarp (#129).
Giovanni's Gyarados sits at 5/132 in Gym Challenge, position 5 of 132. Before it is 4 Erika's Venusaur, and after it is 6 Giovanni's Machamp. The set belongs to the Gym series. It was released on October 16, 2000. The printed size is 132, and the checklist is the same length. The listed rarity is Rare Holo.
The attack Summon Storm lists no damage number. The cost is Water. Flip 2 coins. If both of them are heads, this attack does 20 damage to each other Pokémon (even your own). Don't apply Weakness and Resistance for this attack. Dragon Tornado is another attack lists 40 damage. The cost is Water, Water, Colorless, Colorless. Unless this attack Knocks Out the Defending Pokémon, choose 1 of your opponent's Benched Pokémon and switch it with the Defending Pokémon. Weakness is Grass ×2. Resistance is Fighting -30. Retreat cost is 3.
Gyarados (#130) has 56 other cards in the catalog. Those other cards are in 39 sets. The other printings with a release date run from 1999 to 2025. The earliest other card is Gyarados 6/102 in Base (1999). That card is named Gyarados, while this one is Giovanni's Gyarados. That card lists 100 HP, and this one lists 90 HP. Both list the rarity Rare Holo. Mitsuhiro Arita illustrated that card, and Ken Sugimori illustrated this one. 52 other cards of Gyarados list a different HP.
The illustrator line reads Ken Sugimori. I count 1,112 other cards in the catalog with that illustrator.
Gym Challenge set binder is where a full Gym Challenge set goes. This card fills one slot there. A generation binder holds one card of each species. Gyarados can fill a slot in Generation 1 binder (Kanto). Themed lists that include this exact card are Trainer's Pokémon, Magikarp and Gyarados, Kanto Gym Leaders and their Pokémon, and Giovanni and his Pokémon. I still need this card.
Flip 2 coins. If both of them are heads, this attack does 20 damage to each other Pokémon (even your own). Don't apply Weakness and Resistance for this attack.
Unless this attack Knocks Out the Defending Pokémon, choose 1 of your opponent's Benched Pokémon and switch it with the Defending Pokémon.
Gym Challenge, in the Gym series. It was released on October 16, 2000. The printed size is 132.
5/132. It is entry 5 of 132 in this checklist.
Ken Sugimori. The catalog lists 1,112 other cards with that illustrator.
Rare Holo.
Gyarados #130, generation 1 (Kanto).
Summon Storm and Dragon Tornado (40).