
Tentacool and Tentacruel - S1-E19
Continuity mistake: When Misty watches Tentacruel go back into the sea after Nastina flies off, her bag is in front of her. But in the next shot, it is behind her. (00:18:54)

Tentacool and Tentacruel - S1-E19
Continuity mistake: When Ash wonders where Misty went, the part of his hat that adjusts the size of it changes from red to white. (00:15:46)

Tentacool and Tentacruel - S1-E19
Continuity mistake: When Ash and his friends arrive in a boat to rescue the sailors, Brock's green vest turns black. (00:03:01)
Answer: He is a good guy but just found himself in a bad situation when he worked for Lysander. He didn't want him to harm Ash and his Pokémon when he was trying to get the special bond between Ash and his Greninja to work. He does leave Lysander and go back to being a good person.