The Engorgement Charm (Engorgio) causes the target to swell in size. It was first mentioned by Hermione Granger in 1992, where she suspected Rubeus Hagrid's pumpkins had been under magical "influence." The counter charm is Reducio.
Fred and George Weasley used this spell on their Ton-Tongue Toffees. In the summer of 1994, they "accidentally" dropped some in front of Harry's cousin Dudley, in order to test their new product. Dudley's tongue swelled to an incredible size.
Kevin, the little boy from the World Cup campground used an engorgement charm on a slug with his father's wand.
Hagrid's boulder-sized pumpkins after he used the Engorgement Charm on it
The Fake Moody used Engorgement charms on the three spiders he used in class to demonstrate the three Unforgivable Curses, so that the spiders would easily be seen by the class.
Harry once used the Engorgement Charm on a spider while he, Ron, and Hermione were camping in the Forest of Dean in search for Horcruxes in 1997. Since he had not won the Blackthorn wand's allegiance, the spell was not powerful enough, and it took two tries for the spider to swell up moderately. In the film, Harry used it on a magical flame, made by Hermione, but the flame got too big.