You need both Kyogre & Groudon cards in order to play. Once you have both cards, place both on your Bench
Mega Tidal Wave
Discard the top 5 cards from your opponent's deck. This attack does 30 damage times the number of Energy cards you discarded to each of your opponent's Benched Pokémon. (Don't apply Weakness and Resistance for Benched Pokémon.)
Discard the top 5 cards from your deck. This attack does 100 damage times the number of Energy cards you discarded.