Playing With / Treacherous Advisor

Basic Trope: An apparent ally of the heroes who offers advice and support... up until The Reveal that they were a villain all along.
  • Straight: Professor Percy has been helping the heroes investigate and collect the Prismatic Pearls of Power. However, after they find the last one, he reveals that he was using them all along.
  • Exaggerated: Not only was Percy a bad guy all along, but he's actually Lord Evildoom, someone the heroes had heard about but never met — or, rather, never realized that they'd met.
  • Downplayed: Professer Percy has been feeding information to the Big Bad but he was forced into it.
  • Justified: Percy knew where the pearls were and needed someone to go get them. Why hire a mercenary group when you can con people into retrieving them for free?
  • Inverted:
  • Subverted: It looked like Percy was going to betray the heroes and give the pearls to his master, Lord Evildoom, but he's actually a double agent working for the common good and switches the pearls for fakes that ruin Lord Evildoom's immortality ritual.
  • Double Subverted: ...but then Percy betrays the heroes as well as his former lord, in order to acquire immortality for himself.
  • Parodied: Percy has an Evil Laugh, an Evil Shadow, Evil Hair and Evil Clothes. The heroes STILL don't see it coming.
  • Zig Zagged: It looked like Percy was going to betray the heroes, but he's actually a double agent, but then he betrays the heroes as well, but it turns out that this was to avert the resurrection of the demon guardian of the pearls, but it turns out that he was actually doing it to cause the demon's resurrection...
  • Averted: Percy does not betray the heroes.
  • Enforced: ???
  • Lampshaded:
    Professor Percy: Of course I was planning to betray you all along, why else would I leave my tenured position behind to follow a Ragtag Bunch of Misfits?
  • Invoked: ???
  • Exploited: ???
  • Defied: ???
  • Discussed: ???
  • Conversed: ???
  • Deconstructed: Professor Percy betrays the heroes at the crucial moment, but all the time and effort he wasted hiding his true intentions from them has given them a chance to get to know his weaknesses and they defeat him almost immediately. In his final moments, Professor Percy reflect on how he could have succeeded if he hadn't helped the heroes so much to keep them believing he was their ally.
  • Reconstructed: Unlike Lord Eviloom, Professor Percy isn't inherently antagonistic towards the heroes. He isn't in it For the Evulz, so helping them was a good way to keep the Pearls out of the hands of their mutual enemy, but his purpose for the Pearls is clearly different from theirs, so he betrays them to execute his own plan after Lord Evildoom has been thwarted.
  • Played For Laughs: Professor Percy is rather obviously Lord Evildoom in a Paper-Thin Disguise, but Bob and the others were still clueless... save for Leon, but nobody ever listens to him.
  • Played For Drama: Because they didn't suspect Percy, the villainís plan succeeds, which results in the deaths of several civilians. The heroes, full of guilt that they weren't able to prevent it, have a hard time trusting anyone ever again. During the next crisis, they constantly accuse their advisors and each other of being double agents, and their infighting lets the villain win again.

Once you've collected the MacGuffins, head back to Treacherous Advisor... Sucker.