From Bulbapedia, the community-driven Pokémon encyclopedia.
Giovanni's Love Club is a predominantly type deck found in the Gym Challenge Strategy Guide. The deck is classified as one of the "hard-core" decks in the book, containing more rare cards than the easy-to-build decks.
Giovanni has two of the biggest and hardest-hitting Pokémon in the whole game, so the idea behind this deck is to get Giovanni's Nidoking and Giovanni's Nidoqueen out and smash through any Pokémon that dares battle your "royal" Pokémon. Giovanni's Nidoqueen needs Giovanni's Nidoking backing her up on the Bench before she can do her best damage. (Ah! Young love!) Once the king is behind her, Giovanni's Nidoqueen's Love Lariat attack does 100 damage per attack. Giovanni's Nidoking's no slouch when it comes to attacking, either. His Tumbling attack can hit for up to 70 damage a turn.
Viridian City Gym is a good addition to this deck because you'll spend a lot of time evolving your Pokémon. When Viridian City Gym is in play, you get a free Potion every time you evolve a Giovanni Pokémon. You can even use Giovanni himself to speed up your evolutions to Giovanni's Nidoqueen or Giovanni's Nidoking. If you need to attack with Giovanni's Nidorina, protect her with the Defender Trainer card because she can do a fair amount of damage to herself. Finally, since this is a Giovanni theme deck, we added Giovanni's Meowth and Giovanni's Persian to the deck. What's a leader without his personal pet cat?