Why is it that some anime episodes show a Pokémon's move successfully damaging a Pokémon with a type-immunity to that move such as Normal-type moves with Ghost-type Pokémon and Electric-type moves with Ground-type Pokémon?
It might cause some confusion to us, including anime characters themselves. It was evidenced with Ash in Dancing With the Ducklett Trio! where he commanded Pikachu to use Thunderbolt on Sandile and it had no effect (someone else even pointed out that Ash shouldn't have done that) even though other episodes showed that Electric-type moves were effective against Ground-type Pokémon. Another instance was when Ash's Goomy's Bide in the 55th episode of the XY series, taking into factor its Generation VI effect, easily damaged Jessie's Pumpkaboo even though if I remember correctly Max and Agatha mentioned in the Advanced Generation series that Normal-types moves had no effect on Ghost-type Pokémon when May had her Skitty use Double Slap on Dusclops and Ash had Pikachu use Quick Attack on Gengar.
It might cause some confusion to us, including anime characters themselves. It was evidenced with Ash in Dancing With the Ducklett Trio! where he commanded Pikachu to use Thunderbolt on Sandile and it had no effect (someone else even pointed out that Ash shouldn't have done that) even though other episodes showed that Electric-type moves were effective against Ground-type Pokémon. Another instance was when Ash's Goomy's Bide in the 55th episode of the XY series, taking into factor its Generation VI effect, easily damaged Jessie's Pumpkaboo even though if I remember correctly Max and Agatha mentioned in the Advanced Generation series that Normal-types moves had no effect on Ghost-type Pokémon when May had her Skitty use Double Slap on Dusclops and Ash had Pikachu use Quick Attack on Gengar.