Tentacool and Tentacruel - S1-E19
Revealing mistake: When Brock says, "Ah! Zubat!" his neck is not fully colored in. (00:15:50)
Tentacool and Tentacruel - S1-E19
Revealing mistake: When Brock says that Tentacruel is using Meowth as a puppet, his neck is not fully coloured in. In addition, while Tentacruel was holding Meowth, it was actually a Tentacool that was controlling him. (00:13:39)
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.