Futurama

Futurama was a 1999-2013 American adult animated science fiction sitcom created by Matt Groening for the Fox Broadcasting Company (and later, for the Cartoon Network). The series follows the adventures of a late-20th-century New York City pizza delivery boy, Philip J. Fry, who, after being unwittingly cryogenically frozen for one thousand years, finds employment at Planet Express, an interplanetary delivery company in the retro-futuristic 31st century.

A Head in the Polls (Season 2, Episode 3)
During the Earth presidential election, a political party called the Brain Slug Party is seeking political power to attach brain slugs to everyone.

Raging Bender (Season 2, Episode 8)
After crashing on the Brain Slug Planet, Hermes is assimilated by a brain slug. He attempts to assimilate the rest of the Planet Express crew, and manages to assimilate Fry. Fry's brain slug dies of starvation however due to his lack of a delta brainwave, which is revealed in The Day the Earth Stood Stupid.

The Day the Earth Stood Stupid (Season 3, Episode 7)
A mystic fleet of brains travels the universe and turns everyone into idiots, and now the turn has come to Earth. Nibbler explains her plan to Leela and explains how Fry is the key to solving the attacks by the brains. She enters Nibbler in a pet competition, but loses to the Hypnotoad.

The Beast with a Billion Backs (Season 5, Episode 5-8)
After Bender's abuse of time travel in the previous movie causes a tear in universe, a depressed Fry goes through the anomaly after breaking up with his girlfriend. He encounters a universe-sized tentacle creature, which promptly invades Fry's unverse. By attaching itself to people's necks, the tentacles cause people to instantly fall in love with it. After conquering Earth, the tentacles create a religion, with Fry as its pope, making the controlled worship it as a god. Eventually, Leela is the last person on Earth without a tentacle.

Attack of the Killer App (Season 6, Episode 3)
After Fry and Bender amass over a million followers on Twitcher, Mom activates a device that controls the minds of all those followers (And other Twitcher users).

Tip of the Zoidberg (Season 6, Episode 23)
Surgery done by Zoidberg, predictably, goes horribly wrong.