Devon and Cornwall (Quest for Camelot)

Devon and Cornwall are the tritagonists of the 1998 Warner Bros. animated film Quest for Camelot. They are the two-headed dragon who desire to be in their separate forms and they assist Kayley on her quest to recover Excalibur and save Camelot. They are respectively voiced by Eric Idle and the late Don Rickles.

Why They Suck

 * 1) The concept of them being written as comedic relief characters in the film is very poor and bland where they are mostly unfunny with no interesting personality and are somewhat useless as they don't contribute much to the film. The reason why they are very badly written as comic relief characters is that Warner Bros. is trying too hard to mimic Disney's formula, but failing at doing so without understanding why most comic relief characters worked so well in many Disney movies, particularly from the Disney Renaissance era.
 * 2) *On that topic, both of them and their respective contrasting personalities are basically pale rip-offs of the famous Disney comic relief duo Timon and Pumbaa from The Lion King (1994), but with none of the charm and likability, those two characters had.
 * 3) Most of the time, they pointlessly throw in lots of random pop-culture references without any valid reason whatsoever in a rather poor attempt to be like the Genie from Disney's Aladdin. In fact, they seem to be a rip-off of the Genie.
 * 4) Their song "If I Didn't Have You" not only comes out of nowhere, but it was nothing more than a poor man's take on the Genie's "Friend Like Me" where they, as stated above in WTS#2, throw in several references like Simba's presentation from the Lion King, and references to Warner Bros. owned properties such as Looney Tunes and Tex Avery's Red Hot Riding Hood.
 * 5) Depending on your view, their constant bickering and arguing towards each other can get particularly annoying.
 * 6) Both of their accents are inconsistent. While Devon has an entirely English accent, Cornwall has a heavy American New York accent.
 * 7) In relation to their poor portrayal of being the comic relief duo, several of their dialogue is nonsensical and incredibly stupid.

Redeeming Qualities

 * 1) Regardless of them being a knock-off, it can be argued that their design is cute.
 * 2) Eric Idle and Don Rickles did decent jobs voicing the respective two heads, and they admitted that they had fun together.
 * 3) Even though their song "If I Didn't Have You" comes out of nowhere and is very much a poor man's take on "Friend Like Me", it is pleasing to listen to on its own with some hilarious moments.
 * 4) They do have some character development in the climax where they put aside their grudge towards each other and work together by gaining the ability to flight and breathe fire. This comes into effect when they fly Garrett to Camelot to save Kayley from Ruber's steel men and rescue Ayden by fending off the Griffin. When they do get separated by the magic shockwave from Excalibur and the Stone, they are pleased at first to be at the separate selves that they wanted, but because of their teamwork and friendship, they decide to rejoin and be together as one.

Trivia
According to Eric Idle, he and Don Rickles add-libbed for days, but none of it was used in the final version of the film.