Never Trust a Villain

Sometimes in the Movies or Tv Shows, a heroes or heroines trust the main antagonist in the beginning or the middle until the villains reveals their true nature and the heroes feel betrayed or angry after they trust them that they were noting but a Pawn that they were just Manipulator them to do their bidding.

Like for example: Not to be confused
 * Know each other since childhood until they got jealous of the heroes which that make them evil. Problems that caused the character jealous ranges from love issues, rivalries to be the best, etc. In some case, a character whom became evil was not always turned to the dark side by their own terms, but could also out of influence of other villains, usually from the Big Bad themselves.
 * The main antagonist don't come until later while pretending to be nice with the main protagonist and after they done being nice with them, they go back to be evil to rule the world, etc. In some cases, the hero' allies or even an enemy whom hero fought/captured later warns him/her about the said antagonist's true nature, which made him/her realized that the main antagonist are not worth to be trusted.
 * Sometimes the main antagonist started out as nice until something happened where they turned evil much later in the story. The said incident would be varies depends on the plot itself. For example, Norman Osborn at first until some accident have turn him into The Green Goblin which it makes him evil and try to control it until the evil side have take over him or Harry Osborn was nice at first until he realize that his father died by Spider-Man (which he didn't know that he was killed by his glider) which it make him evil and drinking too much.

Examples

 * King Candy tricking and lying to Wreck-It Ralph about what happens when Vanellope wins the race.
 * Weevil Underwood deceiving Yugi Muto and tossing Yugi's Exodia cards into the ocean during the boat ride to Duelist Kingdom
 * James McCullen decieving NATO to make them believe he has sold them his nanomite warheads, until the GI Joes realise he is trying to steal the warheads back. This in turn leads to Zartan convincing the people he is the US President and the Joes are terrorists.
 * James T. Kirk at first, trusting Alexander Marcus whom help him to avenge the deaths of his superiors at the hands of Khan. However, thanks to his decision to put aside the vengeance and decided to arrest Khan and having the villain to put onto the trials instead, this allowed Khan to warn the hero about Marcus' agenda.
 * Weevil Underwood tricking Yugi Muto into giving him the Exodia cards and tossing them into the ocean during a boat ride to Duelist Kingdom
 * Snow White being tricked by the Queen/Hag into eating the Poisoned Apple.
 * Tirek urges Discord to join forces with him
 * Zaheer lies to Korra to set the airbenders free, but it was the ruse to killed her personally.
 * Cliff Vandercave tricking Fred Flintstone into signing firing notices for all the quarry workers.
 * Lotso leaves Woody and his friends to die, despite being saved by them.
 * Percy betrayed by Diesel 10 who invades the SteamWorks.
 * Jill Young runs into Andrei Strasser but doesn't recognize him as the poacher who murdered her mom and Joe's.
 * Caramel Man 004 is manipulated by Dr. Mashirito
 * Unalaq lies to Korra so she copen the spirit portal at the North Pole.
 * Bill tricks Dipper to give him his body.
 * The Sultan hypnotized by Jafar, who is manipulating him for his own evil and selfish gains.
 * Peridot being betrayed by Yellow Diamond, Peridot didn't want to destory Earth. After she called her "Clod".
 * Royce warned Isabelle not to too kind with Edwin because he's not like what he seemed among them and the others whom sent to Game Preserve Planet by Predators, in which she ignored him until Edwin unexpectedly incapacitated her with poison-coated scalpel. Reasons why Royce warned her about this previously was due to him aware that they and the others were sent due to them capable to be the ruthless killers, and he himself has predicted that Evin would only revealed his true color once he had a chance.