The Starscream/Playing With

Basic Trope: The Big Bad's treacherous second-in-command (or occasionally lower in the ranks), who plots to overthrow him and take his place.
 * Straight: Halgar is Emperor Tyranus's Dragon, but secretly plans to betray him when he's vulnerable and take his place.
 * Exaggerated: Halgar is obviously trying to murder Emperor Tyranus whenever he can. Emperor Tyranus trusts Halgar too much to notice.
 * Alternatively: Halgar plans to usurp Tyranus. Skullgar plas to usurp Halgar. Terillian plans to usurp Skullgar. and so on, and so forth, through Vyshe in middle management all the way down to Rekkr, the trash man.
 * Justified: Emperor Tyranus is unable to defeat the heroes, most of the time revealing his plans to them, giving them the key to thwart his plans. Halgar wants to get rid of him, since he thinks that he will be a much better Emperor.
 * Alternatively: Halgar is promoted to second-in-command by Emperor Tyranus as punishment for a failed coup, so that Halgar will be forced to live under the shadow of the Emperor's greatness.
 * Inverted: The Renfield
 * Alternatively: Emperor Tyranus is plotting to abdicate his position and force Halgar to take his place.
 * Subverted: Halgar seems to plot against Emperor Tyranus, but it's just a trick to lure out other minions who do want to overthrow the Emperor.
 * Halgar's loyalty seems to be faltering, and it looks like he's starting to think maybe he could do a better job... But before Halgar decides it's time to take matters into his own hands, Emperor Tyranus notices his increasing disloyalty and kills him.
 * Double Subverted: ... but once he got rid of competition and earned the Emperor's trust in the process, plans to betray him for real.
 * ...but Halgar actually wins the fight and kills Tyranus, taking his place in the process.
 * Parodied: Halgar carries a freshly sharpened knife at all times that's inscribed with the words "Insert Emperor Tyranus' Shoulder Blades Here".
 * Deconstructed: Halgar's plans to overthrow the Emperor (even if they were justified) actually help the heroes to defeat both of them in the process. Halgar then learns that, if he kept his lust for power in check and remained loyal to the Emperor, the heroes would be crushed.
 * Alternatively: Halgar manages to overthrow the Emperor and defeat the heroes, but he has no idea how to rule the empire, and so economic failures and civil wars ravage the lands, and in the end, Halgar himself is overthrown.
 * Emperor Tyranus has Halgar exceuted for his disloyalty.
 * Reconstructed: Tired of seeing the Emperor losing time after time to the heroes, and putting down all his suggestions and plans, Halgar kills the Emperor and becomes the new Emperor himself. Under his new leadership, the Empire becomes a major threat to the heroes.
 * Alternatively: Halgar realize that Emperor Tyranus is mentally insane and a incompetent ruler and decide that he should be disposed. Halgar does it, takes over The Empire and, surprising, makes a truce with the heroes, which end the war. Halgar then clean up the mess Tyranus made and The Empire becomes a prospering, successful nation. Halgar also create several diplomatic and economic relationships and alliances with the other neighbour nations. The heroes, who were first suspectful at Halgar, accept that Halgar is a good leader and actually become his allies.
 * Zig Zagged: After killing the Emperor, Halgar proves to be a much better tactician and soon has the heroes in retreat. But before he can lead the final assault, he's stabbed to death by Skullgar, his long-loyal Lieutenant who felt Halgar was getting too much of the credit.
 * Averted: Halgar seems to plot against the Emperor, often even talking with other minions about getting rid of him, but he never tries to overthrow him.
 * Enforced: The only way a rag-tag bunch of heroes could realistically defeat the forces of the Empire is if said Empire was fraught with internal strife and discontent and the easiest way to depict it is with the Emperor's second-in-command constantly trying to claw to the top instead of actually winning any battles.
 * Lampshaded: "Many long to be emperor. It wouldn't be odd if one of his underlings planned to usurp his power."
 * Invoked: The Empire encourages disloyalty in underlings, on the grounds that an underling who is strong, ambitious, and clever enough to overthrow the Emperor has every right to the throne.
 * Defied: Halgar proves that he's loyal to the Emperor whenever he can.
 * Discussed: "So, you are just waiting for an opportunity to kill me and get in charge, don't you?" ("Uhm, uh - no?!")
 * As above, but Halgar's reply is a knife to to the chest, a sly smile, and the words "Not any more."
 * Conversed: "Why is everyone in the Emperor's inner circle such a backstabber? You'd think he'd want minions he could count on."

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Too late!