In The Rescuers, Brutus and Nero, Medusa's pet crocodiles, end up turning on her near the end of the film, and are snapping at her as she's clinging for dear life on the sinking steamship.
And Snoops, Medusa's much-abused, doublecrossed sidekick, is able to row away on a raft, his clothes in tatters but relatively unharmed, taking a moment to laugh at her predicament.
In The Lion King Scar is ripped apart by his starving hyena henchmen at the end. Apparently they weren't amused by Scar trying to blame Mufasa's murder and Scar's subsequent coup on them.note Although the hyenas being responsible for Mufasa's murder was technically true, as the movie implies that Scar didn't consider murdering Mufasa until after Banzai asked sardonically whether Scar should kill Mufasa to become king, and initially only targeted Simba for death.
Something similar happens to Scar in the Sorcerers of the Magic Kingdom. He, after being revived by Hades, tricks the Hyenas into believing that he is invulnerable. When he's exposed to not be the case by the guests, the Hyenas decide to abandon him.
At the end of Disney's Hercules, after Hades was punched into the River Styx by Hercules, the spirits that he had trapped in the river (a few of which he had blasted earlier in the movie) dragged him down into the dark abyss of it forever.
Even Pain and Panic managed to get a last laugh over their boss:
Panic: He's not gonna be happy when he gets out of there.
The Secret of NIMH: Jenner's co-conspirator Sullivan, after being mortally wounded by him, redeems himself by throwing his dagger straight into Jenner's back.
Space Jam: After the 'Toons finally win the big game, Swackhammer starts berating and humiliating the Monstars all the way back to the ship. Michael Jordan asks why they're putting up with him like that. They answer that it's because he's bigger... "bigger than we used to be." Righteous payback ensues.
Very literal example in The Simpsons Movie. Homer continuously whips his sled dogs, for the most banal reasons, until they get fed up with it and maul him.
Homer: Why does everything I whip leave me?
A less literal example occurs near the movie's climax, Martin Prince, who at this point, appears to have nothing left to lose since everybody in Springfield thinks they're doomed anyway, angrily confronts Jimbo, Dolph, and Kearny, for all the times they've bullied him and proceeds to beat all three of them with a two-by-four.
Don't forget Kronk turning on Yzma on account of her verbal abuse. Doesn't work out like he planned, though.
At the end The Hunchback of Notre Dame, after being abused his entire life by Frollo, Quasimodo lashes out and calls him out and throws him to the ground. Frollo can only stammer a feeble attempt at control, seeing as Quasi is much younger, much stronger and very angry.
Frollo: Now, now, listen to me, Quasimodo... Quasimodo: No, you listen! All my life you have told me the world is a dark, cruel place. But now I see that the only thing dark and cruel about it is people like you!
In the final battle, Darwin turns on his former crush Victoria after suffering from her manipulation and abuse. He helps the Pirate Captain knock her down a shaft, bringing about her initial defeat and (inadvertently) blowing up her warship, which they were fighting on.
A few minutes later, Polly the dodo pulls off a literal example of this trope when she escapes from Victoria's clutches by biting her in the eye.
In the "Where Are They Now?" Epilogue, we see that the exotic animals Victoria was planning to eat are staked out around the tree she's stuck in, holding plates and utensils and licking their lips in anticipation.
In The Thief and the Cobbler, Zig Zag's bird Phido (which incidentally is a common name for a dog) is constantly starved and abused, complaining throughout the whole movie that he wants something to eat. And when Zig Zag is defeated by Tack and falls into a pit where the alligators begin to eat him, Phido enters the hole and personally finishes off the villain by eating his head.
In the climax of Monsters, Inc., Boo overcomes her fear of Randall to leap on him and distract him just long enough for Sulley to get back up and grab him.