Slaking debuted in Love, Petalburg Style!, where it was staying in Norman's greenhouse with the rest of his Pokémon. It slept throughout the majority of the episode.
Later, when Team Rocket destroyed a fireworks machine that Norman was keeping for his wedding anniversary, he flew into a rage and thus summoned Slaking from inside the greenhouse. On Norman's command, it charged at the terrified trio and violently sent them blasting off with a powerful Focus Punch.
Norman later used it in his Gymbattle against Ash in Balance of Power, where it demonstrated itself as a powerful fighter. With its brute strength, it almost defeated Ash's Grovyle. However, when Grovyle's OvergrowAbility activated, it managed to gain the upper hand and Slaking was defeated.
A † shows that the move was used recently, unless all moves fit this case or there are fewer than five known moves.
In the Pokémon Adventures manga
Slaking in Pokémon Adventures
Slaking first appeared in Brushing Past Breloom, where Norman sent him out when he sensed someone's presence. He had Slaking use Swagger to confuse the hiding individual and reveal them, but the person he had sensed, Ruby, managed to protect himself with Kiki's Safeguard.